My teacher held off introducing us to the subjunctive tenses until our 4th year, because she says that they can be difficult for foreign students to learn. She also thinks that the extent to which an Italian speaker applies the subjunctives is related to the extent of their education!
Cute analogy, but one mia moglie di Calabria is bound to dispute!

Overview

The subjunctive (il congiuntivo) is frequently used in Italian, whilst it is not used much in English - hence the difficulty for native English speakers.

In Italian, il congiuntivo is generally used in a dependent che clause and reflects the wishes, hopes, emotions, opinions, feelings and doubts of the subject - it allows you to express anything that is not a fact.
It’s useful to remember that the subjunctive is a counterpoint to the indicative, the mood that allows you to convey facts and certainties.

The subjunctive is generally used in a subordinate clause within the sentence - generally introduced by che / that, which, who. As always, the verb in the main clause is in the infinitive whilst the verb in the subordinate (che) clause is in the subjunctive.
So, when expressing something that is an opinion, hope etc with a verb in the main clause (the verb to the left of che), place the verb in the subordinate clause (i.e. to the right of che) in the subjunctive.
Spero che loro parlino italiano / I hope (main) that they speak (subordinate) Italian
Spero che tu venga / I hope that you come
Vogliono che io venga / They want me to come

It is mainly used after the following verbs:
parlare / to speak,
pensare / to think,
credere / to believe,
sperare / to hope,
dubitare / to doubt,
non sapere / to not know,
volere / to want,
avere paura / to be afraid

Subjunctive vs Indicative
Remember - not all verbs in a subordinate clause (after che) go into the subjunctive…only those that follow a main clause verb expressing a ‘non-fact’.
(Indicative) Sa che ‘e la verita / He knows that it is the truth
(Subjunctive) Pensa che sia la verit’a / He thinks that it is the truth
(Indicative) ‘E certoche paga lui / It’s certain that he will pay
(Subjunctive) ‘E improbabile che paghi lui / It’s improbable that he will pay

Here are some links that give some more background information. Enjoy!
About.com: Italian language
Wikipedia(as with all the Wikipedia references, this one is very basic. I’ve really only included it in the hope that it gives you something of interest - caveat emptor!)
italian language guide (a pretty thin reference, but it discusses some more obscure use of the present subjunctive)

An general outline of this post:
- Overview
- Common uses
- Regular conjugations
- Regular conjugations (-iare verbs)
- Regular conjugations (-care, -gare verbs)
- Irregular conjugations
- Impersonal expressions
- Subordinate expressions

Uses

The subjunctive is used after verbs and expressions of command, demand, desire, permission, preference, request and wishing.
I’ve listed some common verbs and examples to set out the general framework.

Verbs of desire, hope, preference and will desiderare to wish
sperare to hope
preferire to prefer
volere to want

Desidero che tu legga / I want you to read
Spero che arrivino presto / I hope that they will arrive early
Preferite che io vada al ristorante? / Do you prefer that I go to the restaurant?
Tu non vuoi che noi ti aspettiamo / You don’t want us to wait for you

Verbs of emotion
arrabbiarsi to get angry
avere paura to be afraid
dispiacersi to be sorry
essere contento, triste to be happy, sad
temere to fear

Ho paura che non trovino la strada / I am afraid that they will not find the road
Sono contento che lei sia arrivata / I am happy that she has arrived
Mi dispiace che oggi non ci sia il sole / I am sorry that today there is no sun

Verbs expressing command
esigere to demand
ordinare to order
pretendere to demand
richiedere to request, demand

Io richiedo che vi togliate le scarpe quando entrate / I request that you take off the shoes when you enter
Pretendo che voi mi aiutiate / I demand that you help me
Esigo che usiate la massima attenzione / I demand that you use the maximum attention

Verbs expressing permission
lasciare to let
consentire to allow, permit
impedire to prevent
permettere to allow
proibire to forbid

Io permetto che voi parliate in classe / I allow you to talk in class
Tu proibisci che stiamo fuori fino a tardi / You forbid us to stay out too late The present subjunctive states actions that may take place now or in the future.
‘E necessario che tu beva / It is necessary that you drink (now).
‘E possible che arrivano tardi / It is possible that they will arrive late (future).

Regular conjugations

To form the present subjunctive (il congiuntivo presente) of regular verbs:
(1.) Drop the endings from the stem of the infinitives
parlare / to speak… parl-
vedere / to see… vol-
sentire / to feel… sent-
finire / to finish… fin-

(2.) Add the appropriate endings to the stem
(-are) -i, -i, -i, -iamo, -iate, -ino
(-ere) -a, -a, -a, -iamo, -iate, -ano
(-ire) -a, -a, -a, -iamo, -iate, -ano
(-ire) -isca, -isca, -isca, -iamo, -iate, -iscano

(3.) Add here are the results:
parlare/ to speak
che io parli
che tu parli
che lui/lei parli
che noi parliamo
che voi parliate
che loro parlino

vedere/ to see
che io veda
che tu veda
che lui/lei veda
che noi vediamo
che voi vediate
che loro vedano

sentire/ to feel
che io senta
che tu senta
che lui/lei senta
che noi sentiamo
che voi sentiate
che loro sentano

finire/ to finish
che io finisca
che tu finisca
che lui/lei finisca
che noi finiamo
che voi finiate
che loro finiscano

Regular conjugations (verbs ending in -iare)

For verbs whose infinitives end in –iare (cominciare, mangiare etc), do not repeat the ‘i’ when forming the stem.
cominciare/ to begin - cominci-
che io cominci
che tu cominci
che lui/lei cominci
che noi cominciamo
che voi cominciate
che loro comincino

mangiare/ to eat - mangi-
che io mangi
che tu mangi
che lui/lei mangi
che noi mangiamo
che voi mangiate
che loro mangino

Regular conjugations (verbs ending in -care and -gare)

For verbs that end in -care or -gare, ad an ‘h’ to all forms of the present subjunctive.
giocare/ to play
che io giochi
che tu giochi
che lui/lei giochi
che noi giochiamo
che voi giochiate
che loro giochino

pagare/ to pay
che io paghi
che tu paghi
che lui/lei paghi
che noi paghiamo
che voi paghiate
che loro paghino

Irregular conjugations

As always, we need to consider the irregular forms. I’ve listed some common verbs with irregular forms in the present subjunctive; all of these end with an ‘a’, regardless of whether the infinitive ends in -are, -ere or -ire.
I know there are many other vebs with an irregular form, but I want to keep the post relatively simple to start with…I’ll progressively add more over time.

andare vada, vada, vada, andiamo, andiate, vadano
avere abbia, abbia, abbia, abbiamo, abbiate, abbiano
bere beva, beva, beva, beviamo, beviate, bevano
dare dia, dia, dia, diamo, diate, diano
dire dica, dica, dica, diciamo, diciate, dicano
dovere debba, debba, debba, dobbiamo, dobbiate, debbano
essere sia, sia, sia, siamo, siate, siano
fare faccia, faccia, faccia, facciamo, facciate, facciano
potere possa, possa, possa, possiamo, possiate, possano
rimanere rimanga, rimanga, rimanga, rimaniamo, rimaniate, rimangano
sapere sappia, sappia, sappia, sappiamo, sappiate, sappiano
stare stia, stia, stia, stiamo, stiate, stiano
uscire esca, esca, esca, usciamo, usciate, escano
venire venga, vennga, venga, veniamo, veniate, vengano
volere voglia, voglia, voglia, vogliamo, vogliate, vogliano

Impersonal Expressions

The present subjunctive is used in a dependent che clause after impersonal expressions of possibility, opinion etc.
‘E necessario che tu venga / It is necessary that you come
‘E probabile che piova domani / It is probable that it will rain tomorrow
‘E facile che io vada al cinema / It is possible that I will go to the movies
Bisogna che voi studiate / It is necessary that you study

I’ve listed some impersonal expressions with which the present subjunctive is used:
‘e necessario che / it is necessary that
bisogno che / it is necessary that
‘e probabile che / it is probable that
‘e peccato che / it is a pity that
‘e opportuno che / it is opportune that
‘e raro che / it is rare that
‘e improbabile che / it is improbable that
‘e facile che / it is possible that
‘e bene che / it is good that
‘e difficile che / it is difficult that
‘e meglio che / it is better that
‘e giusto che / it is right that
‘e importante che / it is important that
‘e preferibile che / it is preferable that
‘e importante che / it is important that
‘e possibile che / it is possible that
‘e impossibile che / it is impossible that
basta che / it is enough that
non importa che / it is not important that

If the impersonal verb indicates certainty, don’t use the subjunctive
‘E certo che vengono oggi / It is certain that they are coming today

Subordinate expressions

The subjunctive is generally used with the subordinate expression che, however a number of other subordinate expressions also call the subjunctive:
a meno che / unless
a patto che / provided that
affinche / in order that
benche / although
cosi che / so that
dopo che / after
finche non / until
malgrado / although
nonostante che / although
prima che / before
purche / provided that
sebbene / although, even if
senza che / without

It is also used with the following pronouns and adjectives:
chiunque / whoever
dovunque / wherever
ovunque / wherever
qualunque / whatever