I'm also going to suggest Specialized - the Hardrock Comp. It's frame is designed to mimic the P3. It's inexpensive, durable, and easy to upgrade. Try to find a 2002 model, the price ranges anywhere from $350 to $400.

As far as Schwinn (GT) goes, they were bought by Pacific, the same company that owns Huffy, and because of this you will see them in K-Mart and Wal Mart. They're also trying to keep the "high-end+ bikes in the LBSs, but they won't fare well; people equate Pacific to non-quality built bicycles.