Verb, verbs verbs. Can you ever get enough practice? Here's a very neat little application that gives you lots of straightforward drill practice in a variety of tenses:
About.com is a good source of grammar input and practice. There are lots of 'worksheets' with accompanying answer sheets so you can try out exercises and then check your own answers online - or print them off if you prefer. If you get completly stuck, there are forums where you can ask questions. I've always been very impressed by how well and how quickly my questions were responded to - all by volunteers, so be polite!
This simple but well made set of pages gives learners lots of practice in some of the basics of Italian grammar that need lots of lots of repetition:
nouns: gender and singular/plural.
articles: definite and indefinite.
The exercises aren't just useful for beginners; in fact I would say they would be of most help to learners with an Intermediate level and above who want to consolidate.
There's also a section on Italian numbers - not just the straightforward bits but the fiddley bits as well.
The following site calls itself: Il Sito Del Verbo.
There's lots of explanation and reference material here. However, the most useful part is the'Eserciziari' - lots of verb/tense exercises that you can check for yourself. Sensibly it allows you to use the apostrophe instead of an accent in most cases. With all of these self-correcting online sites you have to accept that sometimes you will input a correct answer but be marked as incorrect because the author had not anticipated your answer when building the exercise. If this happens, just chalk it up as a moral victory ;-)
Christina Mazzoni has made a fairly comprehensive website to support her learners' understanding of Italian grammar. This site is more thorough and easier on the eye than most I have seen and includes exercises to consolidate learning.
On the next page you'll find some links to some other useful stuff.