I think that apart from some old scanners (I mean old pro scanners that run inly via SCSI with G3 Macs and similar) your only choice are the current flat bed scanners - Epson V700/V750 or Microtek M1/F1.
If you require enlargements beyond 4-5x that still show full detail you will need to get you films scanned by a lab with some kind of Imacon, but otherwise the above mentioned scanners should give you decent results (when you learn how to use them properly).
I have the Microtek F1 (which I got as refurbished, otherwise I would have got the V750) and use it for 6x6 and 4x5" and, with some tweaks it can do a decent job. I did some 35mm scans too, but found that to be a waste of time as these can be scanned cheaply by a lab that uses Coolscans.
The F1 has it quirks (especially the software - I expected more from Silverfast, honestly), but it can deliver decent results. Just check my flickr - there are quite some samples - even with 100% crops.
If you need to find out more be sure to browse also the
LFF forum as many guys there have similar problem (namely locating a decent scanner)
good luck