Without a doubt, Virgin Mobile's new all inclusive prepaid plan is the best!
25 dollars a month gets me unlimited text/mms/video, Web, and 300 minutes of call time. No activation, no contracts, no connect fees. I'm on month two and I love it so so so so much.
There are other levels as well-I believe 40 dollars a month gets you an additional 900 minutes or so to the call time.
I had tried NEtTen in the past, and they were ok. However, 300 minutes would have cost me $30 and no extras like text or web.
I can't express to you how much I love Virgin Mobile's new unlimited plans. It has saved me SOOOOO much money. Their customer service can be a bit to deal with, but we can deal for unlimited at $25 a month.