Pros: GREAT price, decent service
I've got Sprint's 'SERO' plan. SERO stands for Sprint Employee Referral Offer, and it is (officially) open to anyone who knows a Sprint employee. I knew someone from college.
The SERO plan is great... you get basically unlimited of everything Sprint offers, except for minutes, and it is about $30/month. That's unlimited picture and text messaging, unlimited data, Sprint TV (although not all the channels), etc. etc. All for $30/month (500 minutes)
Sprint's coverage is decent enough that I don't have problems with dropped calls too often. They're leading the major companies in terms of their 3G data buildout, with 3G service having been operational for some time in most markets. Data is fast, although I've seen better.
Customer service is the usual mess that I've had with pretty much every cell carrier I've tried (AT&T, Verizon, and Cingular (before they were bought). Nothing special, but nobody has anything special.