Years ago I discovered Gixen for myself and haven't had to look any place else. I tried other services and even ran programs on my computer, but Gixen is the only thing I've found that works well for me. I've used it for every bid in every auction without fail.
I especially like the grouping function so I can be sure that I'll win one, and just one, of several auctions for similar items. Gixen helps me save money, and for that I'm thankful.
I would tell more people about Gixen, but I don't want them to have my secret tool!