I'll second the Playbook mention. I have some HD650s plugged directly into it, no amp or other gear, and it drives them pretty well. More than enough volume for my needs (Although I do admit I listen to my music quieter than many people), and the sound quality's nothing to complain about and...

Hi, Head-Fi.   I've been lurking around here for a couple years and I'm still relatively new to high-end audio, having just upgraded from a PXC-450 and Total Bithead (My first "real" headphones and amp) to some HD650s. My current setup is my PC with an Auzentech Forte for the sound card...