I like the 20FPP $1k Turbo freerolls. They're fairly quick, and easy enough to cash in, though I've personally never had the good fortune to make the final table, the payout is certainly nice for the 1st-9th. Over the past couple days I've cashed twice, each time for about $2.50. Can't say whether or not that's a good exchange of FPPs to cash, though.
As for Full Tilt, I've posted this elsewhere, but I think the Daily Dollar satellite and Ferguson satellite are the best two freerolls to play. The rest of the public freerolls have been, in my experience, very, VERY hard to cash in. Doesn't stop me from trying, though I think trying to build my bankroll up through freerolls is actually hurting my SnG and MTT play in some ways. The satellites, though they only run once each per day, are fairly quick - Daily Dollar is a super turbo, Ferguson is a turbo. They also have the added benefit of getting you into MTTs that have a pretty good payout structure, despite HUGE fields.
Just my two cents on the freerolls though.