I know plenty of folks running 37's on 3.5-5" of lift. 3.5-4.5" and you'll likely need to trim the fenders.
You'll definitely need to re-gear, and you'll need a programmer to adjust the computer/speedo. 5.13's for a 6-speed, and 5.38's for the auto, in the JK. I also HIGHLY recommend the Superchips as the programmer.
Beyond that, if you're running a non-Rubicon, you'll want to swap out your Dana 30, or at LEAST beef the HELL out of it (trusses, sleeves, C gussets, etc.), or it won't last worth a damn.
Also, at that level, you'll obviously want to add front and rear lockers (push-button).
You'll likely want hydro-assisted steering as well, as factory steering craps out fairly fast with 37's.
Beyond that, there's always something else to buy!