I've been playing with TextPayMe.com and it's pretty cool. You send someone money by texting "pay 5 1231231234" where 5 is the amount and the rest is the number. Then you get an IVR call in response to confirm by entering in your PIN code. Then the other person gets cash. Signing up is just like PayPal did back when - you get $5 free.
Feel free to send me some cash to test out the service. (They've also got a contest to win an XBox 360... based on referrers, so sign up then add your own banner on your too!) :-D