http://www.parktool.com/products/det...=25&item=HCW-5

this is the tool used most often. There is also an "adjustable" one that has a hinge but it's not needed usually. The HCW-5 is fine.

Get a set of metric allens at home Depot, from size 4 to 6 at least. You can get a lot more torque from them than a multitool.