Well, IMO, nothing beats Deep Exploration, but it's far from free.
As for totally free, I haven't seen any good ones around for a while, maybe there aren't even any. Probably not any you could rely on consistently for complex objects.
However, Accutrans is very good, and it's only 20 bucks, but you can use it free for 30 days.
I use Deep Exploration, but did try Accutrans, and it does a really good job.
www.micromouse.ca/