I think these are all the Micro SD types on amazon:
sd hc
sd xc
sd xc mobile ultra
sd xc ultra
Are all these types compatible with the Clip Zip ?
I read somewhere that Rockbox can be installed, and the Micro SD card can be formatted to FAT32,
as I’d like to get a 64GB Micro SD card.
Officially, only SD & SDHC format memory cards are supported. You can re-format the SDXC cards (64GB) to FAT32 and use them, even with the original firmware. Rockbox is not necessary, but you may run into the database limitation if using the OF, depending on how many files you put on it.
I wouldn’t waste my money on the Ultra series. It’s a “faster” card, but you don’t need that with an mp3 player, only a digital camera taking HD video and such.
“ultra” and “mobile” are just product names, not real things. If they only sell “mobile ultra super turbo black label edition” in that size, then just buy it.
For the OP, note, also, that you don’t have to buy a SanDisk card–other cards should work as well, from other manufacturers. (Having said that, the Zip, in the past, has had some issues with some cards from other manufacturers, although this bug seems to have been fixed (although I’m not sure if this has been fully handled)–I’d always make sure that you can return, if needed.)