[Johnny Angel]

Provide a variety of challenges. A tweaked out combat monster will thrive in a game where combat is often the only viable option for solving problems; likewise, someone who is optimized to do something else will thrive in a game where whatever that 'something else' is is the only viable option for solving problems. I've found that providing a variety of situations and challenges is the best way to prevent someone from overshadowing the rest of the party. Being exceptional at one thing usually means that your skills are lacking in a different area.