I've been experimenting with Dwolla lately. They charge $0.25 per transaction over $10 (and nothing for under $10). The downside is they skip credit cards and go straight for your bank account so you a) need to hook up your bank account to them (which I did for PayPal anyway), and b) unless you have money hanging out in your Dwolla account, paying someone takes 3 days for the bank transfer to clear (which, again, is going to happen with PayPal anyway if you use a bank and don't run a balance, like me).

My only real problem with Dwolla is their iOS app sucks, and their website isn't a whole lot better. But I've had no problems with their actual service, although I've only transferred a few hundred dollars so far.