Sandisk Extreme-III/IV cards are the best, fastest flash memory cards around. They've been verified to run 30 and 45 MB/s both ways, respectively. Also, class ratings are virtually meaningless; they only ensure bare minimum rates of 2/4/6 MB/s, which even worthless counterfeit crap from Hong Kong can reach. There're also tons of deals to make them affordable; I got three 8 GB extreme-IIIs for only $32 after rebate (which might still be useful if you can find them on an eligible site) from a recent
slickdeals.net post. I already use an ultra-II MSPD (15 MB/s r/w, $52 on Newegg) in my PSP, and it kicks ass, so these should be even cooler.
Edit: Looks like extreme-IV speed isn't available in SDHC yet. Still, it's out there in CF cards for you to be jealous of the people who can afford it.
Truth.