If $500 is your budget, the Nikon D100 is too much at $1999 without the lens. I'd try to save another $500 and go for the new Nikon 5700. The images are pro level and its priced at $999 or lower online.
Canon has the G3 out which is supposed to be great though I've only seen G2 pics and don't think they are as good as a Nikon.
There's a new high end Kodak out at 14 Million pixels that is supposedly at beyond film level in terms of the file size it can generate. Not sure of the model number though.
The Sigma SD9 produces incredible pics with the new Fovean chip but its running over your budget also and is priced in the D100 range.
I just bought a Nikon 4300 for $499 and the images are top notch as close to fine as any pro camera I've seen samples of.
The only time you need pro level is if you are doing print work. For the Net I've not seen anything past 1600 x 1200 and the only site that really goes that level in a big way that I've seen is alsscan.com. I don't know what camera they use, but they produce some of the best looking pics out there. Check this out for example.
http://www.alsscan.com/budapest/miastone002.jpg