I think that you should go to the OG when you're done. Really, the only books you need to do well are a prep guide and the OGs. It's a good idea to do the prep guide first, since (as you'll see when you start working problems) the explanations in the OG are often terrible, especially for quant.

You might also want to pick up the OG quant and verbal supplements for additional practice. Anything more than this and you're probably sacrificing quality for quantity.

Jim, Thanks for the great advice. Is the Princeton Review GMAT good enough for a prep guide or should I purchase another prep guide such as Manhattan SC?

Since I work for a different prep company (Veritas), I'll reserve judgment on that question and let others chime in.