AniDB is non-profit database of anime information that is freely open to the public. As well as providing general anime information, if you sign up you can organise your anime collection, keep track of what you've seen and how much you liked it, and all kinds of nifty extras.
To get your own MyList started, you can either add files you have on your harddrive, easiest by hashing them with an AniDB Client, or use a generic for anything you've seen in a cinema or own on DVD. Read full details for more.
Even without a MyList, you can vote for various things in AniDB: anime, episodes, groups - and comment and vote on groups releases of anime and reviews in the database. If you vote for the anime you've seen you can use the anime hint feature to see what else you might like to watch.