Apple has launched iTunes Preview, which is a means of showing what music is available on iTunes right in the web browser.

This seems like an incredibly obvious way to do it, and one that many have been waiting for way too long, but now if you want to look at the iTunes catalog, without having to install iTunes, you can do so. You cant listen to song previews without installing iTunes, but at least you can see what they have. You do still have to download iTunes to purchase music. According to MacWorld, the feature only works for music, but could probably be applied to video at some point.