ATT GoPhone.
You can choose your plan. (see
https://www.paygonline.com/websc/rat...ateplan_en.jsp)
I like it a lot, very flexible, and the 100 MB data for $20 should cover a month of emails and casual browsing. If you go over the 100mb, you could always buy more...
I found their coverage was stronger than TMobile's in my area.