I have a Vortex SPARC and it comes with a screw in 2x magnifier, but I think it's real close to useless. I don't have any other experience with Vortex magnifiers.
I'll second the recommendation for a 1-4x scope though. I use a Burris but I really like the looks for the new Nikons and excellent prices too. If you don't need the 1x option, then there's a whole world of 2 or 3x to whatever scopes in your price range. The M223 Nikon looks great but the new P223 models look even better.