This is a very good area to get into. There are plenty of options available here. I have a few different systems myself that are on the go in NRL and they all are quite good.

One interesting tidbit I can provide is that for most of 2007 and all 2008 I just put a flat amount on any NRL team offering $3 or more for the win. It made a pretty good profit.

I've stopped doing this one as I have developed my own rating system which defines odds and then I look to get "value" on these (i.e. find teams offering more than my estimations predicted). So far this system is 9/16 and making a healthy profit. So it goes to show that there are plenty of ways to exploit these as most punters dont know how to frame the market properly.

Good luck.