For those of us that still need to hone our chops, the Cafe Walter HA-1A paired with a good set of headphones is about as great a tool as any. This Practice Amp can be used either with an included A/C (U.S.) Adapter or with two (2) 9-volt batteries (not included).
You can read more about these here:
http://www.cafewalter.com/ha1/index.htm
The one that I am selling is as-new in the box with everything EXACTLY is it came from Cafe Walter Audio. I originally bought two because I wanted to have a back-up, but since these are so bomb-proof, I am selling this one so that it can be put to good use!
$125 plus shipping OBO. New they were $170 when I bought them (plus shipping) and they are usually on backorder and hard to get!
Cheers,
Jason