As a Monk you'll primarily (probably exclusively actually) be a melee class, fighting with your fists. As such you should invest heavily in Constitution and, to a lesser extent (because of the strength-boosting items in the game), Strength.
Intelligence and Charisma are a distant 5th and 6th. Unless you end up with excess stat points after maxing out your main stats, just keep Intelligence and Charisma at 10.
As for specifics, I'd do this (and in this order):
Assign 10 points to each stat. Max out Dexterity. Max out Wisdom. Max out Constitution. Max out Strength (if still possible). Dump final stats (if any) into Charisma.
Remember though that it's ultimately up to you what finally happens. It's YOUR game, after all.
"War is delightful to those who have not experienced it." - Desiderius Erasmus http://www.gamerevolution.com/features/violence_and_videogames
"Max out Dexterity. Max out Wisdom. Max out Constitution. Max out Strength (if still possible). Dump final stats (if any) into Charisma."
Sorry but this is very misleading. The monk is a 3rd edition class and thus in BG2 its not fully implemented, thus wisdom does nothing. Intelligence is useful for mindflayer protection and it's economical to have it in a multiple of 5 plus 1 (6, 11, 16). Con is optimal at 16 and dex at 18. Although there are str belts in the game its still better to have 18 str too. Seeing as you get an 18 cha ring straight after leaving Chez Iren it's nearly always the least important stat.
"Yes, exceptional strength bonuses apply to unarmed attacks."
Last time I played a monk was years ago but I'm pretty sure monks don't get an exceptional str.
18 str 18 dex 17 con (only need 16, but wait!) 12 int 11 wis 18 chr
This allows you to wear Keldorn's armor, which really helps during the early levels. The con, int, and chr are a must, but I don't remember the other requirement (maybe 15 str?). If you don't want to equip the armor, max str, dex, and take con to 16. The rest is just gravy. If you max str at 18, there is a quest later that can boost it to 19, which really helps damage. Hit points from Con and AC from Dex are self-explanatory.