Honda shadows, yamaha vstars etc... are all good choices. Just dont get in a rush, find something that is clean and has been maintained with regular oil changes, valve adjustments etc...You can find bikes that have been knocked over in driveways by there beginner owners for cheap and with low miles usually. If you want to put in some wrench time, Honda CB as mentioned make sick bobbers as does the yamaha xs650. If your not keen on slightly more maintenance, or if you plan on riding in a variety of elevations or conditions i'd recommend picking up a newer bike that is fuel injected. Little more money up front, but you wont have to worry about rejetting the carb and other issues that come up.
Here's a 01 vstar 650 I found for $3900, there cheap and the possibilities are endless, hardtail bobber, brat style with stock suspension etc...