When I was researching head units last year, I was convinced that Eclipse was the best bang for the buck (a lot of buck, but a substantial bang to back it up). They have very good D/A converters, very good FM tuning (one of the best quality tuners on the market) and a good security system. I also like their appearence - not too flashy, nice color, good spectrum analyzer.
Nakamichi makes an AWESOME head unit. Their top-of-the line MB-100 has a 24bit D/A converter with analog preamp. It holds 6 discs in the head unit. Very business like. (Probably very heavy - I never considered weight when I was looking before).
MB-75 (similar to the MB-100, without the nice preamp):
Someone on another board mentioned the JVC KD-SH909 which has a 24bit D/A converter, can play MP3s, and has a fancy tuner. A *bit* flashy, but not too bad & kinda matches the aluminum interior of the Elise
...anyway, those are the ones that have impressed me the most