Looks like they've upped their game, many more offerings now. Each one has a 5k bonus after 2 months and 2 points per $.
Marriot Rewards, Priority Club, Starwood Preferred Guest, Wyndham Rewards, Amtrak Guest Rewards, AAdvantage, Skymiles, True Blue, Mileage Plus, and Dividend Miles.
HHonors gets 3 points per $, and so does OnePass if you have a Continental credit or debit card.
I actually got an offer from AA with a 7500 bonus, so I think I'm gonna do that, but otherwise the frontrunners would have to SPG, then maybe Hilton or CO.