http://www.atangeo.com/buyWin2Yesterday I find this tool, not it's free, but the cost really it's about 26€, it's a poly reducer, extremelly good and easy yo use...
The technology it's use in Daz 3d, I suposse whit the Decimator plugins, and it's awesome...
Yesterday I did a simple test, from 96000 Polys to 20.000 (this can do better if you divide the mesh in parts smartly, and after apply the process)
http://www.atangeo.com/buyWin2I leave you a couple of images...
I think this comes fine for if anyone buy or download free models, and have a lot of polys, and don't have to much idea, or simply you don't want make a retopology...
PS: I find another OpenSource but not it's too much recomendable*** because you have to know whats means the mathematical concepts, and really I make the same test and crasesh...
*** The good thing it's you can paint over the models, like I do whit BodyPaint, but for free, I suppose not it's too much powerfull but it's the best way for texturing 3d Objects...
http://meshlab.sourceforge.net/