I picked up an Arion Tubulator tube screamer clone for $20.00.
This thing is incredible. I've used it behind my Vox Pathfinder 15R and my 65-watt Kustom combo amp and it's given me the best tone I've ever had.
I know it's cheap, I know it's all plastic, but man, does it sound great! I can only imagine how it would make a really good amp sound.