It's used in a number of cases. It's a long topic, so I'll try to be concise.
Subjuntive is used with verbs that express doubt, as you already know:
Sembra che (it seems that...), credo che (I believe that...), penso che (I think that)... and so on.
Non sono certo che (I am not certain that...), dubito che (I doubt that...).
It's used with verbs that express hope or fear:
Spero che (I hope that...), temo che (I fear that/I am afraid that...) and so on.
It's used with verbs that express desire:
Voglio che (I want that...), desidero che (I desire that...) and so on.
It's used with verbs that express feelings:
Sono contento che... (I am happy that...), mi fa arrabbiare che... (It makes me angry that...), mi dispiace che... (I am sorry that...).
It's also used after che in impersonal forms:
It is possible that... è probabile che...
It is needed that... bisogna che...
It is impossible that... è impossibile che...
It's used with indefinite pronouns:
Wherever you go... dovunque tu vada... (instead of vai)
Whatever he says... qualunque cosa lui dica... (instead of dice)
After some conjugations:
Although it is easy... nonostante/sebbene sia facile...
As if he were here... come se fosse qui... (note: English has retained subjunctive here!)
It's used for referring questions during indirect speech:
She asked me if you had a pen. (Lei) mi ha chiesto se tu avessi una penna.
And let's not forget these:
If I were rich, I would buy a ship. Se fossi ricco/a, comprerei una nave.
Hope this helps!