MilkShape handles OBJ files quite nicely. The trial software is a 1.6MB download, and you have 30 days to try out the fully-functional program before the save features are disabled. Registration is only $20.

Two caveats:

1. It currently won't handle anything over 16000 polygons (it doesn't like the Millennium figures' heads, either)
2. It's a simple polygon modeler; no splines, boolean functions, or other advanced features

Other than that, it's great for Poser-work; I've created props, figures, and morph targets for Posette, the P4 Male, and the reduced-resolution version of Victoria.