Cheers, mbassist is pretty well known about but it is certainly useful.
There are a few other free odd matching tools available. Here are the ones i know about.
oddsmatcher (OddsMatcher : bet72.com Risk Free Betting) - another website based tool, a bit like mbassist.
newbetsfriend (new bets friend) - a application the you download and scrapes the odds live. In beta so a bit clunky, also only a few bookies.
rebelbetting (RebelBetting) - another application. Only does dutching. Runs in the background and alerts you at intervals with the current best matches. Still in beta but has been well tested.
Umm thats all i can think of off the top of my head. Any others out there?