Aside from buying a prepaid plan, the best option is probably T-Mobile's Basic Plus plan that offers 300 anytime minutes and unlimited weekend minutes for $29.99. Keep in mind, however, that 300 minutes isn't much. The other carriers all offer basic 450-minute plans for $39.99.
Best value for people who receive a ton of calls but rarely make them:
Sprint's Free Incoming plans are unique in that you're only charged for outgoing calls. Incoming calls, by contrast, are completely free. Obviously, not everyone will find such a plan worthwhile but it's great for users who want to stay in touch without actually doing the touching. Prices start at $49.99 for 300 outgoing minutes and max out at $99.99 for 1,000 minutes.
Best value for messaging fans:
Verizon's Choice Select plans offer unlimited text, picture, video, and instant messaging for an extra $20 per month over the company's traditional voice plans. Given the popularity of text messaging, this is a no-brainer for many phone users.
Best value for people with a few really close friends:
Do you spend most of your minutes talking with just a few people? Consider T-Mobile's myFaves plans that let you select five people for unlimited chatting, regardless of which carriers they use. The myFaves plans generally offer fewer anytime minutes than similarly priced plans from other carriers, but because conversations among your "five" don't count as anytime minutes, it's easy to come out ahead with a little monitoring. Note that myFaves plans don't offer mobile-to-mobile minutes, however.