what kind of sd card should i get for my dsi?

I found this answer on a forum:
SDHC is just considered to be SD 2.0 (very much like USB vs. USB 2.0). Much in the same way that USB works on a USB 2.0 port (at USB 1.0 speeds), SDHC is not backwards compatible to SD reading devices. But an SDHC slot will read an original SD card; conversely, an SD slot will not read an SDHC card. (someone correct me if i'm wrong). SD High Capacity is anything over 4.0 GB, and I believe that the maximum current capacity available is 32 GB.

Because Nintendo did not mention specifically that the slot would be SDHC, it is highly likely that the media slot on the DSi will be only SD compatible, meaning that the memory allowance for expandable memory would be capped at 4.0 GB.

I found some SD cards at these great stores for you:)
    
DreamGear DGDSI-1933 Media Kit for Nintendo DSi - SD Card and Reader
The Media Kit includes a USB SD Card Reader and 2GB SD Card for transferring music, photos, and data from your computer to your DSi gaming console using any computer with a USB input.
Not sure if you would be interested in a starter kit but here ya go:)
Intec G1984 Dsi / ds Lite Starter Kit with Sd Card
Kit includes:
# Earbuds
# Screen protector films
# Cleaning pad
# Car charger
# Hard polycarbonate case that holds 4 extra games, 2 secure digital cards(tm) & 2 styli
# Secure digital card(tm) & case