How about $30 Data Plan?
You might consider the following no-contract data plan from T-Mobile which I think is a very good deal: For $30 a month, you'll get 100 minutes, unlimited text, and unlimited data (the first 5 Gig at 4G speed then throttled?). The good thing about this plan is you can bring your own smartphone (T-Mobile smartphone, or any unlocked GSM phone), order a sim card, activate the sim card and choose the $30 data plan.
Even though 100 minutes are not that much, but if you go over 100 minutes, they will charge you 10 cents per minute. To compensate for your minutes, you just need to use WiFi and Google Voice on your smartphone to make free calls (anywhere in USA and Canada!).
So with this data plan plus WiFi, you basically get EVERYTHING UNLIMITED. I think you cannot get this deal with any other carrier. The great thing about this T-Mobile plan is that you have the total freedom to choose your smartphone and the plan that fits your budget, and you are not tied up in a two-year contract that, I believe, most people dislike. That's my 2-cent opinion.