Photo student looking to buy a used digital camera. Any advice?

I'm looking to buy a new (to me) camera this summer and I don't want to make a decision without doing research. I will be graduating from college soon and I need to upgrade so that I can build a decent portfolio and have a nice camera to work with when I look for a job.

I currently have a Nikon D50, handed down from my mom, and a few decent lenses. Therefore I'm mostly interested in Nikons. I was looking at the D90 and the D300. I want the best thing I can get and my price range is under $1100 for just the camera body.

Does anyone have any advice on these two cameras or anything else that I might be more happy with?