Need a prepaid sim for data for Mexico

[tl01]

What is the best place to buy a sim for Mexico before we leave for a trip? I only need data. Are there any places that sell the sims here in the US. I used to live in San Diego... Maybe I should have checked before I moved...

 

[minicard]

I've used them for a trip to the Philippines without any problem.
http://www.cellularabroad.com