There are plenty of great slr's out there. I used to shoot Nikon, but now I shoot Canon. I do alot of High ISO low light and IMO Canon has less noise. But both are GREAT cameras!
I shoot freelance for some pros...and they ALL tell me the same thing..NEVER buy new equipment...your probably going to end up upgrading soon enough so dont buy new.
You probably want to stay with Nikon or Canon. Reason being...its not the camera that makes great pics...its the GLASS! (and the photog but good glass with make an average photog look great) And Canon and Nikon have tons of lens out there, it will be easier to find used lens and there are just more options.
On that note, I suggest the Nikon D40, or the Canon 40D.
also check out kenrockwell.com
http://www.kenrockwell.com/tech/recommended-cameras.htm
That guy is awesome!
Another place to find good stuff is fredmirand.com in the buy & sell forum.