Micro SD Cards for the MobileMapper 10
The 'User's Manual' for the MobileMapper 10 recommends that you use SANDISK Micro SD cards.
After some user complaints, last week I purchased a few (nearly 75) cards:
and it is my personal opinion that the 'Transcend' brand is a MUCH BETTER CHOICE. Here are the SD Card Facts as I know them:
  Most 2-GB SanDisk cards work
  Some 4-GB SanDisk  cards work, some don't. I can't visually tell the differnce.
  No (none) 8-GB SanDisk cards work
  EVERY SINGLE Transcend 4 GB and 8 GB card that I tested worked with no issues
For background, there is a little 'C' on the cards:
Inside the 'C' is a number: 2, 4, 6 or 10. (In the image above, there is a 6). The number is the 'Class' and higher is faster. '6' indicates that the card will write 6 million bytes per second to a card in a fragmented state.
The HC stands for 'High Capacity'. The original cards were 'Standard Capacity' (SC). There are also SDXC (eXtended Capacity).
There are reportedly over 400 brands of SD Cards and over 8,000 card models. I only tested SanDisk and Transcend.