I've spent quite a bit of time comparing cheap options. MMM likes Google FI, which can be a good value for low data users. Here are a couple of my other favorites:
Visible: Can get unlimited Verizon 4g service (Data, minutes, text.) for $25 per month (Base price is $40 per month, but if you sign up and then go to Reddit "party pay", you can get future months for just $25.
Catches. 4G only. Only works with certain phones. - They sometimes offer rebates on signups for new customers. Overall a huge bargain if you can get over the phone limitation and have good Verizon 4G coverage. (Should be expanding.)
Tracfone: Once known as a pretty horrible company (Better coverage now, still awful support.) , is now one of the largest prepaid providers. For persons just needing light usage, they have some annual plans that are hard to beat. (Take a look on Ebay.) Also they have a monthly 1gig plan ($20) that beats Google Fi's price if you don't need the international features.
MintMobile: A pretty good value if you have good T-Mobile coverage in your area. They are also giving unlimited data through 4/14 on all their plans. $15 per month for unlimited talk, text and 3GB high speed data.
http://fbuy.me/oU4PYI've found Mint Mobile support to be comparatively better than many Post-paid companies. Please consider using my link if interested.