You didn't specify whether you wanted a dedicated film scanner or not. If you want a dedicated film scanner, see if you can still find a KonicaMinolta DiMAGE Scan Multi PRO (they've been discontinued) and then purchase the aftermarket Scanhancer 5LE. You'll have a hard time beating it even with an Imacon scanner. If you can't find the Multi PRO, the Nikon Coolscan 9000 is a close runner up. Expect to spend around $2000 for either one, though. The Imacon scanners are excellent but, being a Hasselblad product, are pricey. Go for one if it's going to pay bills or make money for you.
If you don't require a dedicated film scanner, you may wish to look at an Epson 4990 or 4990 Pro. I recently purchased a Pro because of it's ability to scan 4x5 (and larger) negatives and slides. I'm not sure yet (still testing), but it seems to be giving me results that are as good as, if not better than, the quality of the Multi PRO for medium format. I ran it and the Microtek i800 side by side for two weeks and ended up keeping the Epson. The only downside to the flatbed scanners is that they are a good bit slower than the dedicated film scanners.