MyAnimeList.net is a site for cataloging and ranking (and discussing, but...) Anime and Manga you have read/watched, collected, etc. I have one and tend to find it useful to keep tabs on all the series I follow.
my gosh! this might actually be useful! I once used some kind of "loan monk" website or something for keeping track of my anime. However the library feature maxed out at around 500 titles at which I promptly stopped using it.
Here's my list! Took me a good minute to think of them all--not only the ones I own, but the one's I've seen before or owned previously, but traded in.