Word on the street is that the R4 team did not release the "R4DS SDHC" cards that you've been seeing on the market... IMHO, 2 gigs is a hell of a lot of space though. Certainly plenty enough for me. If you really want more though, I'd do a bunch of research before buying any card that claims to support SDHC.
PS.
I've got an R4 and I love it!