Foster-9, if you're looking for used amps there's a lot of selection:
Any Krell amp. There are several Evolution 302s available, as the 302e just came out. The older FBPs are great too. Any higher power than a 300-series amp just seems like overkill to me.
Any Levinson 33x or 43x-series amp, or any later models. My one caveat with Levinson is that service can be complex and expensive. My 334s have been bullet-proof, but in current dollars remember that even the low-end 334s would likely be $10K each.
The Parasound JC-2. These have always tempted me, and they are occasionally available used. They were $3K each when they were introduced in 2003, but now they retail for $4500 each.
Bryston, Ayre, Pass Labs, Classe, Coda, Boulder... mostly North American stuff, since high current amps seem to be a largely western hemisphere thing. Of course, these are all very expensive amplifiers. For used equipment there's a good economic argument for Krell & Levinson, simply because there's an active market and these amps retain high resale values. Any of them will be costly to service.
New high-current amps that claim to double power with halved impedance seem to start in the $5K range and go up. Way up. Krell and Levinson seem to think $20K amps are mid-range nowadays. Mostly I think what we're paying for is fancy aluminum casing work and Swiss-watch-class build-quality in a North American factory. (Most of the components will be imported.)
IMHO, the most important spec for a properly design solid state amp these days (well, at least the one I look at first) is signal-to-noise ratio. Almost everyone has low distortion and high power, but noise is a different story. Most amps are rated at something like -100db below full power, and since they usually have 25-30db of gain we're talking in the range of -70db of noise, sometimes worse, below 1 watt of output, which can be audible with some speakers, especially if the frequency distribution of the noise amplitudes include a good bit of output below 20KHz. Maybe it's just me, but I find a dead-quiet background attractive. The latest Krells are very low noise, for example, the older Levinsons less so.
