"Best" would probably be a professional CRT monitor, like the Sony PVM series. The most common one you'll find available in a usable size would be the 20" PVM-20M4U, usually in the $200 range +/- $100 depending on condition. There's a 25" version that's much less common, which would be a lot better, and a lot more expensive. I have read that, although there are PVM's bigger than 25", they're not really any better than standard consumer-grade Trinitron televisions. Don't know if that's true or not, and they're pretty rare anyway.
"Normal enthusiast" solution would be a good quality TV from the last years of CRT, with composite, s-video, and component input. I prefer conventional curved screen types, but a lot of the TV's from those last years were flat screens. With a good JVC, Sony, Toshiba, etc, that shouldn't be a problem. But on cheaper brands, the flat screen CRT's actually had a cropped display, so beware.
Also I would add that the Wii looks best on a CRT, provided it has component input AND is genuinely capable of 480p display. I have a 36" JVC that can do this, and the Wii looks amazing on it, much better than on any HDTV.
edit: I think you're better off hitting a few pawn shops and craigslist than trying to find something on amazon.
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