It all depends on what you are looking for, wether or not you want to sacrifice your current cell phone number and the region you are in.
Here is what I tell most of the employees at our company that are looking for "Family" cell services....
Look into At&t's "Mlife"- They offer reasonable plans with excellent coverage and the Customer Service is very good. Stay away from the GSM phones (for now, the coverage is still not that great). Cell phones offered by AT&T can be purchased through promotions that usually wind up giving you the phone/phones for free, extra minutes, voicemail, call forwading....etc... Grant it, you may have to haggle a little but "everything is negotiable".
Another provider is T-Mobile.....I'm not crazy about this former "Voice Stream Wireless" company (Customer service and billing was pretty bad). This provider is also a PCS provider with OK coverage and average plans. You would realy have to do more research on this company.
Hope this helps!