I went with a Donald North Audio Sonett. I read all I could for months to find what amp matched well with the HD800 headphones and decided on tubes, and I was very close to buying a Woo Audio.
But in the end decided that the DNA Sonett was a better option for me at the moment.
http://www.dnaudio.com/

I'm very pleased with the end result.
Part of my decision for the Sonett was the fact there aren't too many tubes, and I knew I'd get sucked into the tube rolling thing. And I did, but because there's only two tubes, it's not too painful on my wallet.
As opposed to something like the Woo WA22, with its 5 tubes, or the WA2 with 6 tubes.

Edited by Eee Pee - 4/23/11 at 9:48am