With the monk, I'm fond of sticking to unarmed strike (you'd be at 2d6--2d8 next level--with Ascetic Stalker, right?) You could also grab a monk's belt to start off at 2d10. I'm also fond of using Improved Trip with Combat Reflexes and Flurry of Blows. Against large groups of medium or smaller bipeds, you can generally expect to successfully trip 3-4 opponents, gain a free attack on each (at +4), and attack each one a second time when it attempts to regain its feet. At 15th level, this tactic will generally eliminate multiple swings by affected oponents as well, which therefore nets you a threefold benefit (+4 bonus on follow-up attacks and allies' attacks, 3-4 extra attacks, and a reduction in the number of attacks opponents can make). With 8d6 Sudden Strike dice, you should also consider Improved Feint (although you'd have to give yourself a higher intelligence score). Improved Initiative is an obvious choice, as is Weapon Focus (unarmed strike or whatever else you decide to use), and perhaps you should also consider Weapon Finesse with a higher dex than strength.
If you decide to stick with 12 con (I always put my highest score in con), you should definitely consider Improved Toughness, which I would consider even with a high con score. Power attack, Cleave, Great Cleave is usually a good choice, too. Fiery Fist from PHB II gives you an extra 1d6 fire damage for 1 round by expending a stunning fist, and Vexing Flanker from the same book is just an outright great feat (+4 attacks when flanking).