My favorite band I think is Dream Theater, which was greatly inspired by rush to be progressive. Or so I've heard, at least. Rush is defiantly up there with my favorite artists, but I only have two of their albums.
How do people feel about progressive metal? Like Between the Buried and Me, The Human Abstract, Mastodon, and other stuff like that? It's a lot heavier than traditional progressive (which I usually like more) but sometimes it's really awesome to hear such heavy riffs and pounding beats played in odd time signatures.