Technogirl, I say, skip the multi-tool. They are a gimmick.

You need so few tools when you are on the road that you might as well get a dedicated tool for the job.

Any mechanic will tell you that to do a job, you need good tools. Multi-tools are a compromise at best.

Make your own excellent tool bag with the following:

1) at least one 6" adjustable wrench (check to make sure your bike even has a use for one first).
2) Tire patch kit with tire irons or "Milk Levers"
3) Allen wrenches specific to your bike's needs (probably two or three is all you need)
4) multi-head screw-driver.
5) chain tool and a couple of spare links that match your chain.
6) Check your brakes and derailures to see what tools you might need to make adjustments.
7) Give your bike a good look-over and look at every fastener (nuts and bolts). Make sure you have a tool for each of them.
8) Wrap some duct tape around a pencil so you have both some duct tape and a pencil when you need it.
9) a couple of plastic zip tabs (electical fasteners) come in handy and weigh nothing. Get them at the hardware store.

It looks like a long list and a lot of stuff, but it will all fit in one hand. If you are a weight-freak, then this list might seem insane, but there is nothing worse than being stuck on the road without the tools to fix a simple problem.