Here's a thread on xda-developer forum of working MicroSD cards list

http://forum.xda-developers.com/showthread.php?t=834144

Confirmed Working(Data remains after soft reset):

Centon 8GB Class 6

Kingston 4GB Class 4

Kingston 16GB Class 4

Microcenter 16GB Class 2

Patriot 16GB Class 2

PNY 8GB Class 4

PNY 16GB Class 2

SanDisk 8GB Class 2

SanDisk 16GB Class 4

Currently Unstable/Unsure:

Kingston 8GB Class 4

Kingston 32GB Class 4

SanDisk 16GB Class 2

SanDisk 32GB Class 2

Confirmed Not Working(Data gone after soft reset):

A-Data

A-Data 4GB Class 6

A-Data 8GB Class 6

A-Data 16GB Class 6

Lexar 16GB Class 6

Transcend 8GB Class 6

Transcend 16GB Class 6

Also, just found Patriot 16GB Class 4 on Amazon, it now claims it works on Samsung Focus

http://www.amazon.com/MicroSD-Memory-Samsung-Mobile-MicroSDH...