+1 for USBasp.
I have an authentic MKII but never use it since the cheapo programmer also powers my breadboard.
I'll chime in on the AVR bandwagon too. I have lots of boards. Altera, ST, Cypress, PIC etc and usually end up playing around with Atmel chips since they are easy to use, cover the simple stuff very well and have TONS of code floating around on the internet for common tasks. Great learning tool IMO even though the competition is cheaper and more advanced.