Hotels: I've only found Hyatt worthwhile. All programs transfer 1:1 but Hyatt tops out at 30k points for the top tier hotels vs 60k+ for the other programs.
Flights: Lots of useful transfer partners. awardhacker.com is a good place to start to find out how many miles are required by each program for a specific itin. Watch out for fees tho... you wouldn't want to fly to London on BA.