This deal has ended.
Buy.com has the 4GB Kingston SDHC Card for $21.95, one of the lowest prices I have seen. Shipping is free and there's no sales tax (except CA, MA, MD, TN). Of note: if you have never used Google Checkout, you can sign up and pay via that service and get an extra $10 discount. SDHC stands for secure digital high capacity, so make sure to confirm your device is compatible.