Two flashes at roughly 45 degree angles to blow out the back wall (which was a slightly off white) and you will want to flag these to keep any light from landing on the back of your subject. Then I light the subject with a simple softbox on a boom arm to get a simple clean look like this:

The subject stands roughly where the white X is and then position the camera right in front. You need a fairly decent size room for this but I often find a hall works well. The main this in distance between the back of the subject and the wall to avoid spill off the back wall.

Here is a roundup of some of the best tutorials on achieving this style of image.

Zak Arias White Seamless Tutorial Part 1, 2, 2b,  3, 4, 5

Building an infinite white wall (for video but will work for stills as well

Lighting Infinite White from Videopia on Vimeo.

Seamless White Background @ Home Tutorial from Scott Bourke on Vimeo.