PayPal is the obvious option. 232 million accounts and all that, with the option to withdraw by ACH, check or free debit card. There's even no fees if the recip

PayPal is the obvious option. 232 million accounts and all that, with the option to withdraw by ACH, check or free debit card. There's even no fees if the recipient only has a personal account. You can use Mass Payment to do payouts in bulk. Lots of companies that run affiliate programs pay out commissions through PayPal using Mass Payment. I don't usually recommend it, but this seems like a good use-case for Dwolla as well.