there are a ton of online and mini programs that will convert OBJ files to STL.. I haven't played much yet but they are out there.

Hexagon does.. I've uploaded a few items to a 3D file share for printing http://www.thingiverse.com.. I do it there cause it does a virtual image/print of the item so you can see if there are any errors...

Places like SHapeways does it also.. 

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Hexagon, Carrara, Sculptris, and recently Sketchup.