SD cards won't go beyond 4GB, that's why SDHC exists and can go up to 32GB. Unlikely to see 10GB cards as the capacities are doubling 1/2/4/8/16 etc.

Quite reasonable prices on 4GB SDHC cards here. The microSD option is quite interesting as not only is it cheaper than the full size card but will probably prove more useful in multiple devices (eg. N800 and/or a mobile phone). I doubt the Class 2/Class 6 speed difference will make much difference in practice.

I've bought both 4GB and 8GB SDHC Transcend cards (both Class 2) from this vendor and have been very happy (am not related etc. etc. just a happy customer!)

The Transcend SDHC cards work very well with the modified high-speed SDHC kernel, unlike my 4GB SDHC SanDisk card which isn't capable of high-speed mode.

Just a word of caution - be very, very careful when buying flash memory on eBay... my advice: don't do it.