IBM has used T420's for under $400, and a T410 for $296. The best deal looks like a T420 with a i5-2520M processor, 8GB of RAM and a 160GB hard drive for $307. All of them are 14" screen Windows 7 Professional. Let me check Lenovo for new 15"...
ETA: New 15" laptops from Lenovo start about $600, and a Win 7 downgrade is still available but $50 extra. (I only looked at a couple of models)