Travelling to the US and need cell data - any ideas?

After T-Mobile's announcements yesterday, I'm a little more confused. What is the best option for someone travelling to the US for a month, and wanting data access?

At first it seemed like T-Mobile's UnCarrier initiative was going to be my saving grace but after doing a bit of research I'm not too sure. Basically, last summer I spent a month in Los Angeles but I hadn't even thought about getting a SIM card so I suffered in silence with no data or cell access.

However, this year it should (read: probably won't) be easier to organise now that I have a Nexus 4. From looking on the carrier sites, it seems T-Mo is the only one to sell a SIM-only off-contract data package. So can I just buy the T-Mo SIM and pay it once then cancel it once I leave? (Even though $60 for 2GB seems a bit steep)

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via cl.ly

Am I missing something or is there just a much better deal I haven't even spotted? Any help is greatly appreciated.