I've had pretty decent luck with e-rewards. You aren't going to earn miles quickly, but can pick up a few thousand miles a year that way.

As of right now, MyPoints lets you redeem for United miles, and also offers Marriott and Hyatt gift cards.

Swagbucks doesn't have a miles redemption option right now, but you can redeem for Southwest gift cards. (They seem to be the quickest redemption option these days- hit their surveys just right, and it could be a $100 GC every six to eight weeks.)

iRazoo (there's a conga to get a membership here somewhere) has Travelocity hotel GCs.

IIRC, there are times when AA miles show up as a redemption option for Coke points. Coke also rotates Priority Club points with Hilton and other hotel programs as a redemption option.