Both Fairlay (
click for link) and BetBTC (
click for link) are sportsbooks and also betting exchanges, though I've personally never used either of them and they don't seem to have a lot of volume from what I can see right now. I don't currently see any active scam accusations against either site so they should be safe to use (BetBTC's thread dates back to Nov 2014 and Fairlay's to July 2014), though please feel free to correct me if I am wrong.
Leo you are truly wonderful! I will check out them links,many thanks!
OP, you took the words out of my mouth, also a long-time Betfair user and can't believe there isn't a booming BTC betting exchange yet.
Good links from leowonderful, I have checked both those out already... they are the best I could find but let's just say they both leave a lot to be desired. Be interested to hear what others think about them. Also if any others on here use Betfair or another of the fiat exchanges.