This introduction to the present tense conjugation of the irregular verbs "dar", "ir" and "estar" is easy to understand and includes a short test at the end to test the student's mastery of this grammar principle.

This site from Tex's French Grammar provides a concise explanation of the subjunctive mood, listing some verbs that have irregular formations in the subjunctive. Brief explanation of when to use focuses primarily on "il faut que"...

This site from Tex's French Grammar clearly explains the uses, formation and negation of the passe compose, using high quality examples, dialogues, (both written and audio), and interactive exercises. Contains link to usage with avoir as...