If I was using SD cards, I'd just buy a bunch of SD cards! 4GB runs around $5 these days (maybe $10 for a premium high speed card). Even with CF cards you can find a decent 4GB card for $8 and premium cards for maybe $15.
Transcend 4 GB Class 6 SDHC Transcend 4 GB 133x CompactFlash I often carry a netbook PC which I paid $199 for and it has a 160GB hard drive. Cheaper and more useful than an iPad. I use a USB card reader with it. This one has 320GB
Acer Aspire One AOD270-1410For even less than that you can get a 500GB hard drive with built in card reader -
Digital Foci Photo Safe II PST-251 500 GBOn a recent trip I just used cards. I used up 24GB of CF memory in my EOS 7D (shooting RAW+JPEG most of the time) and I didn't come close to filling an 8GB SD card in my P&S. I wasn't shooting video though. That can really eat up memory.