If you're considering used, then I'd look at the Bryston 3B-ST(125 W), Monarchy SE-100 Deluxe(100 W), and Belles 150A Hot Rod(125 W). All three of these amps handle difficult loads extremely well, double output as impedence goes down, and have a clean, balanced, non-fatiguing sound.
If you are patient, all three can be found for $1,000 or less here on Audiogon.
If you are patient, all three can be found for $1,000 or less here on Audiogon.