simple mobile: $40 unlimited everything
simple mobile's $40/month plan now includes unlimited 3G data. so that's unlimited talk, text, and 3G data for just $40 per line. that's nearly the cheapest deal you'll find anywhere in the US right now.
walmart family mobile: unlimited talk and text, free data for 3 months
the first line is $45/month, so this isn't the cheapest plan for those who only need one line. but every line after that is just $25/month, so this can end up saving a lot of money if you need multiple lines.
data is free for the first 3 months (for those who sign up before the end of 2011), and after that it's pay-as-you-go, which means this is also for those who need little or no data. note that the unlimited data offer doesn't include picture messaging, but each new activation gets 100M free data anyway, so the picture messaging will probably come out of that.
t-mobile: $30 unlimited text and data
this one's kind of strange: you get unlimited data (the first 5 gigabytes are at 4G speeds, the rest will be slower) as well as unlimited texts, but you only get 100 minutes of talk. I suppose if you text and use the web a lot, but hardly talk, this would work for you. another possibility would be to use this with a service that lets you make free data calls, such as whistle phone.
virgin mobile: $35 unlimited text and data
much like the t-mobile plan, this one gives you unlimited texts and data (the first 2.5 gigabytes at 3G speeds), but only 300 minutes of talk.
republic wireless: $20 unlimited everything
yeah, you read it right. $20/month (technically $19) for unlimited talk, text, and data. there is a pretty big catch though: republic wireless enables prices like this by offloading your mobile traffic over wifi. what this means is if you do most of your cell phone usage (whether it be talking, texting, or web) within distance of a wifi signal you have access to (for instance at home and work), then republic wireless can save you a hefty amount of money. if you can't meet that requirement, however, I wouldn't recommend it. the best part is you get 30 days to change your mind and get your money back.
these plans all do require you to buy your phone up front, but with the money you'll save paying these kinds of rates (the most expensive plan mentioned here is $45/month), you'll be able to afford a nice phone. the best part (other than saving a lot of money, of course), is that all of these plans are contract-free. no more dealing with crummy customer service or paying more than you like because you're locked into a contract.
what are you waiting for? stop reading and go save some money!