Fender MT-10 "Mini-Twin" practice amp for electric guitars. 1 watt, $40.
Eventually I'll want to get a nice Marshall or Fender two-input amp in the 30-40W range, but for my current skill level this is plenty of amp. And supposedly it can sound pretty good given the size (only slightly bigger than a VHS cassette). Don't even have to plug it in - it runs off a 9v battery!