esnipe is good...I use it all the time, saved me hundreds. Costs about 50pence per successful winning bid, but nothing if you dont win the coin(s)
There are free ones and pay ones. The one I use lets you set a certain number of snipes at any one time for free, and if you want to have more "live" at any one time, you have to pay. I think it's $5 a year. www.gixen.com