I have an Edirol R09 and would recommend it from a sound quality point of view. It has very good built in mics and handy one (well two actually) touch recording and can record in .Wav or .mp3 and I think other formats.

Negative points are I think its relatively expensive, not that unobtrusive (I think of it as the size of a shaver) and when its recording it has a bright red light on it - not great for making sneaky recordings but I know none of us would want to do that anyway!

Mine can't handle an SD card bigger than 2 gigs, but its now about 14 months old - newer versions may be able to handle the larger cards.