It's only fair to do more than just mention the Mesa Baron. I understand that this amp created a stir at the last Stereophile show as well as at the recent WCES, and for good reason. It sounds terrific--a perfect contrast to the dryness of much solid state. The Baron also allows you to tune its sound, from full pentode to triode in 1/3 increments, with varying degrees of feedback. All of this flexibility is not a gimmick--it works and not to the detriment of the music. There is one drawback though. The Baron provides a lot of gain, and depending on your preamp, this may make residual hiss more apparent. My CAT Signature, for instance, was a terrible match in this regard; the hiss intruded on the music. But this amp would be great with a passive linestage, and I had good results using the Meridian 518 between my transport and DAC and no preamp. In fact, the combination of the Baron and the Meridian (with its many different dithering and shaping modes) would give you a system whose sound you could change in a seemingly infinite number of ways.
My friend Grant has the wonderful Aerial 10T speakers; he found the Baron to sound flabby with them, especially in the bass. Compared to the Thiel 3.6es, the 10Ts are a bit dark, and from what Grant has told me, they need megawatts to really come to life. The best I've heard the Aerials has been in Grant's system, driven by a 400-watt NRG Control amp (that's no longer made) so big it should've come with wheels. I'm not surprised the Baron sounded painfully tubey with the Aerials.
The CAT and the Baron may've been hissy, but they made beautiful music. Together they gave the music more body and dimensionality than I've ever heard in my system, and they really opened up my CD collection, making most anything enjoyable. Although the Baron is not the most transparent amp I've used, it more firmly planted the music in my room than any other amp, so who cares?
I give the Baron a strong recommendation. Its flexibility and sonic charms are hard to improve on, and to sweeten the deal, I understand that when it comes time to retube, Mesa will sell replacements to the original owner at half price. I've noticed that a number of dealers have been picking up the Baron, so you'll have a good chance of getting one for audition--wherever you are in cyberspace.