I just ordered some OCZ secure digital cards from NewEgg.com. They are a reliable company so I thought I would post here. I have an A-Data card in my laptop for readyboost and I haven't had any problems for 6 months. I'm not sure how OCZ and A-Data quality compare to SandDisk or Lexar though. 2 cards can ship via usps for about 2.50. I'm using the 2GB for the internal and the 8gb for the external. Here are the links with prices:

$9.49
OCZ Speed 150X 2GB Secure Digital (SD) Flash Card Model OCZSD150-2GB - Retail

$29.99
OCZ 8GB Secure Digital High-Capacity (SD/SDHC) Flash Card Model OCZSDHC6-8GB Class 6 - Retail


$9.49
A-DATA Turbo 2GB Secure Digital (SD) Flash Card Model Turbo SD 150X 2G - Retail

$29.99
A-DATA Turbo 8GB Secure Digital High-Capacity (SD/SDHC) Flash Card Model TurboSD SDHC 8G - Retail

I've been using two OCZ 8gb class 6 cards for a couple of months now, so far no problems.