Here are a few DSLRs in your price range to compare features. There are full reviews for most of them. Good hunting.
Bottom line.. Any of these will be a great camera for you and take excellent pictures. The Pentax, Canons and Sony have a ton of used lenses available at great prices--Sony bought Minolta cameras and the old Minolta lenses work on the Sony bodies. With Nikon, you need to move up to the D80 at least to take full advantage of the old lenses. The Olypus is a new system, so not much if any used stuff.
I'm getting a camera just because I don't have one and I'm tired of taking photos with my 3 meg cell phone. I've been researching that Best entry-level digital SLR cameras list here on the site and trying to figure out which is the best for me. I guess its gotta be between 500-700 dollars and that's it really. I just want a nice camera for whatever. I'm not a pro or anything... just for fun. Thing is when I watch the videos there's always an upside and a downside to each one... which makes the choice sooo much easier...NOT. Any suggestions? Thanks.