I'll toss my overly biased and perhaps hackneyed opinion out here on this one.
PPI Art or PC series amps. They're pretty cheap on ebay (especially compared to how much they sold for new). When parts blow, they're easily fixable and replacement parts are cheap. They last a lot longer than modern day amps anyway, so repair is rare with them. I've tried with modern amplifiers in the same price bracket (MTX, Alpine, Rockford Fosgate, etc.) but I just can't find anything that matches the price-for-quality of the oldschool PPI amps (maybe other oldschool amps?).