Greenevil has a good suggestion. Record your normal rhythm guitars twice and pan hard left and right. Then record rhythm guitars two more times, but this time try changing something in your rig. A different guitar, cabinet, amp, effects, or micing. Then pan that hard left and right and blend the volumes. This should give you a very large wall o' sound. Be careful and play the parts exactly as the one before it, the different takes will give you a nice chorus effect, but can be mushy or muddy sounding if done poorly. If using distortion, turn down the gain level on the amp and record slightly less than you normally play live, this helps reduce the mush...
http://www.soundclick.com/bands/pagemusic.cfm?bandID=294119
This link will show you the exact sound I got by using this method. I used a Trip Recto 2 ch into a Marshall, using a SM57, and Fender Fat Strat. First take was Mesa all the way, second take I added a Boss SD-1 Pedal and changed the cabinet. Hope you like it...
This method works really well for heavy rock, as the guitarist from the 80's hair bands swore by this.