I'd second Delicious Library. I picked it up after getting an iSight, and really appreciate some of the features in it. A big one for me is the exporting of the library to an iPod, so I can quickly check my podcast playing Nano at the store to see what DVDs I already have, as I have been prone to buying things twice accidently or skipping something because I thought I owned a movie an old roomate did.

Combine it with a free web exporter and your library can be seen anywhere. Some people posted libraries in the comments section of that post.