ZTE Blade/San Francisco memory cards that work
I found this discussion at MoDaCo about the issue.  It includes cards that people have tried and found to work.

The generally consensus seems to be that Sandisk 16 GB Class 2 cards work.  Kingston 16 GB Class 4 worked for a couple people, but not for another until they tried deleting everything on it via Windows XP.  I personally wouldn't go lower than a Class 4 card, and I'm partial to Kingston.