I have not tried it myself, but I would not recommed getting many Rogue levels. The monks abilities get drastical better as he gets high level, and many of the things the rogue can offer will get covered by the Monks abilities. (Evasion and Imp.Evasion).
You might be able to gain a little by the Sneak Attack from the rogue, and it will help you to survive traps in the early game, but once your Monk gets highlevel you can all but ignore traps (especially reflex traps with Imp. Evasion
)
I would rarely multiclass a Monk with something personally.