I use gixen for sniping. It's web-based and free.
However, getting the last bid in doesn't guarantee you will win. If an earlier bid had an higher maximum than your snipe, that will win regardless of when you submit your bid.
The best thing about sniping is avoiding the bidding wars. When a bunch of people are manually submitting bids over the course of a few days, the prices can get quite out of hand. People will go over their "maximum" because it becomes so tempting to be the winner.