Um...how 'bout Marriott.com, HHonors.com, SPG.com, etc.? Start there - find your best available fully-cancelable points/perks-earning rate and book it.

Then go on your quest through Orbitz, Expedia, Hotels.com, Travelaxe, Travelocity, etc., etc., etc. looking for something better. Chances are you'll find it, and then you can decide how much hotel points and elite-status perks are worth to you.

Don't totally rule out Priceline. I know it is weaker abroad than it is in the US, but just because someone else couldn't get it to work for their dates doesn't mean you shouldn't try it for your stay. If Priceline is a viable option for this particular trip, certainly research that angle and consider making some bids.