Just figured I'd let you guys know about this, since a lot of people don't like the idea of having to cut holes in their carts, plus having an SD card stick out looks a little goofy anyway.
I also know some of you guys were using half-height SD cards (aka RS-MMC) but those weren't really ideal since they topped out at 2GB, they never made microSD to RS-MMC adapters, and the little adapter that converted it to regular SD was terrible and snapped off all the time.
I found this dude and while it took a few weeks to get it (he custom makes them) I can now report it works wonderfully:
http://cgi.ebay.com/ws/eBayISAPI.dll...:X:RTQ:US:1123
There is some very strong clear tab installed so that you can pull it out of your SD2SNES or what-have-you very easily. And if you plug it into an SD reader, you can remove it easily by pushing it in with something (I personally use another SD card I have laying around) and then just pull on the plastic tab he installs!
I have a nice 32GB microSD card housed in my FFVI SFC cart with NO holes and NOTHING sticking out. I bought that on a whim so now that I used it I can say it works perfectly and I highly recommend it!