The absolute best recording device you could get would be:

Creative Jukebox 3

-optical/analog line in(optical for digital recording from a pre-amp)
-20gig/40gig models
-with new firmware, auto cuts up recordings, or you can mark them
-full wav capability
-interchangeable batteries, so that you can change on the fly during recording
-best sound quality out of any portable player

I have fully tested the recording and it does a very good job. I also know a few people with this thing in Kingston who record rock shows

The only other competition would be the Iriver H320/340. Has a line in, but the North American versions don't have full WAV capabilities, and it just doesn't sound as good.

If you want really top notch quality, you are going to have to by pass any portable player/recorder. The circuitry just is not big enough to hold fully developed DACs (digital to analog converter) and ADCs(analog to digital converter). Most of the time the recording features are just put in to get your attention, but they are not for the hard core.

The Creative is your best bet, before going industrial.