For wheels if you want to stay with the factory width of the bike then you will need to stay with the factory 11" rear wheels. The best 11" wheels would be the OMF wheels which are available with either reinforcement rings or Bead locks. The only other problem is there are only a couple tires made in 11". Maxis Razr or Kenda Kutter's for dirt and I know there are a couple sand tires available as well.
As for the front you have many options as they are 10" and everyone offers them. Many people are changing out there 21" front tires for 23" tires.
I am planing on getting 23" Razr 2's for the front and 22" Razr's for the rear on factory sized OMF wheels with reinforcement rings and beadlocks.
Hope this helps.
2008 700XX - OMF Beadlocks w/Billet Centers & Reinforcement Rings, Kenda Kutters, CCP Steering Stabilizer, ASV F3 Levers, ODI Rouge lock-on grips, Houser Bounce Nerf Bars, Pro Armor skid pad, UNI Filter
2007 400EX - CCP Steering Stabilizer, GT Thunder 450R Shocks, 450R Rear Brake Conversion, YFZ450 Front Brake Conversion, ProTaper Bars, Rath Racing Nerf Bars, Alba Elite Bumper, ASV F3 Levers, ODI Rouge lock-on grips, UNI Filter, Kenda Kutters, Pro Armor skid pad, Armadillo Swing Arm skid pad