Currently using 4 GB Kingston Mini SDHC cards in my Nokia N800.
I notice the mini card will come out of the SD adapter. Almost impossible to get the adapter out of external card. Can change mini card OK. But a problem non the less.
The internal card does not have this issue.

I was going to say buy SD cards but light bulb just went on that you have an N810 which has mini card standard.

I find the Kingston cards are quite a bit cheaper than Sandisk and class 4 and higher have lifetime warranty.

Al