Buy.com has the 8GB Kingston Class 4 Secure Digital High Capacity Card on sale for just $18.95. This flash card is considerably faster than standard SD (you'll notice this both when using the card and when transferring data off of it). Be sure to check that your device and/or computer is compatible with SDHC (versus standard SD). Shipping is free and there's no sales tax (except CA, MA, MD, NY, TN). Amazon also has it at this price, but you need to spend $25 for free shipping.