J.
We recently got basic Pella vinyl windows through Lowes. They were about the same price as the non-name-brand vinyls a local contractor quoted us last year. Also, another specialty window place I called wasn't really interested in our small job (only 3 windows) and recommended we go to Lowes. I was surprised that they also sell wooden windows and have a pretty decent selection.
I didn't realize until after we bought them that Energy Star windows can be deducted on your taxes (I think it's up to $500 or so.) So make sure whoever you use can provide a receipt/brochure that has the Energy Star logo on it.