Well I'm currently clearing FullTilt's %100 first deposit bonus (pretty much strictly through SnGs), and I'd say it clears $20 every 10 or 20 games. Not bad, but I'm sure you could find easier ones out there.
I will be able to clear my pokerstars bonus easily. I will probably be able to get about half of my Full Tilt bonus and the Absolute maybe more than half. Poker.com is the worst - I will probably never see any of it if I understood their explanation correctly. Paradise was always the best because there was no deadline for clearing it. I received all of my bonus money from them before I cashed out. But if you are in the US you can forget them.
Easy bonuses to clear via SnGs: Stars (about 71% rakeback when playing tournaments), bodog (100%+ rakeback when playing only tourneys).
Absolute and Paradise were horrible bonuses to clear via SnGs/Tournaments (10% rakeback - bleh!).
Titan, CD (when I played at those sites) were 40% rakeback when used for tourneys, and Full Tilt at 42% isn't terrible (when combined with a rakeback affiliate, an even better deal).