I LOVE Pinnacle. Good limits can hit. They leave the matches up untill they actually start. Prompt grading. Everyone pales in comparision.
Others.
Olympic - Don' t play there, but the poster Santo said they are useful
5Dimes - most variety, doubles, challengers, allows parlays, game betting. I personally hate them, but most people really like them.
Bet365 - Huge juice. Tons of in-progress betting. Set betting also offered
WSEX - Good for Slams for futures and interactives.
I am American so people outside the US have soooooo many other options including Betfair and I assume other good outs. Hope this helps.