I have posted some arbitrage bets here before.

This doesn't work as good as people say it can because :

1. Some International Sportsbetting agencies are corrupt and its hard to get your cash out of them.
2. Those that offer the crazy odds usually have a maximum payout of up to $20.
3. Its illegal to bet with a bookmaker not licensed in Australia (well it is in NSW).
4. There are people who already run software that automatically scans every bookmaker every 2-5 mins looking for opportunities so opportunities are rare and don't last long.

So now I have given all the bad news this is where it works.

I have found numerous opportunites on Saturdays markets on a Friday night by checking Sportsbet, centrebet, ias, etc fixed odds for the saturday racing. You then check betfair markets for the enxt day and see if there are any opportunities. There are usually one or two if your lucky.

But on sporting events ... I can say I have only found 1 or 2 opportunities ever.

Good Luck.