When I imagine a fighting monk, I´ve the saolin-monk in mind like in "shaolin temple" - and these guys are armed most of the time.
Weapons an armed monk could use:
http://upload.wikimedia.org/wikipedia/commons/7/73/Jian_%28sword%29.jpg
jian sword: a quite thin bladed sword used in tai chi, the basic fighting style resembles fencing and uses the sheath as a kind of conterweight and for parrying
bo quarterstaff: monks are already able to do flurry of blows with quarterstaffs but I´d consider adding feats like cleave or whirlwind attack and lunge to a bo oriented combat style and some kind of whirlwind stance that blocks arrows and thrown weapons
wax wood spear: a very flexible spear - you can bend it for almost 90 degrees. the combat style is a little bit like the bo combat style, the basic attributes of such a style should be speed and range
guan dao glaive: basically a oriental glaive.
dragonwell sword: a heavy scimitar-like weapon - maybe for twf
more exotic weapons:
snake tongue dragon spear: some kind of spear with a flame shaped blade and two half moon shaped blades - maybe a double weapon with reach?
monk spade: better watch this video: http://www.youtube.com/watch?v=7kCzXIFGUqY - a quite odd weapon, style maybe like bo style
twin tiger hook swords: basically hooked blades, two weapon fighting style with trip option?
chain whip: got a hook - so a style concentrating on reach, trip and disarm would fit
three section staff: some kind of big nunchaku, resembling the dire flail, maybe just a "usual" monk weapon with no complex battle style, just like the quarterstaff as it is now
some site I found with google showing pictures of these weapons: http://www.shaolinchimantis.com/Brochure-M/broPage8-SCM.html
In addition, monks should get huge boni on combat maneuver defense, saolin gunfu contains many katas for instantly standing up when laying prone, also saolin monks train to use their chi to destroy staffs hitting them, see: http://www.youtube.com/watch?v=apiT5vSJ6eM&feature=related (don´t try this at home) and they balance on the top of a spear with their bellies
combined styles:
maybe monks should be allowed to use two entire different weapons at the same time, watch this for a dao sword combined with a chain whip: http://www.youtube.com/watch?v=vHwGAZ-vwzs&feature=related
also inspiring: http://www.youtube.com/watch?v=7qHL2PSpecI&feature=related