Went shopping at my local REI and found two solutions that seemed like they would work. Couldn't make up my mind between the two of them, so I bought them both!
The first one that I found was the Nathan Sprint Handheld. This is a 10oz flask. A few nice features include the reflective material, easy to use velcro adjustments, and a nifty race cap with a one way automatic closing valve.
I have used each of them a few times and found them both to be quite effective. They are small enough not to interfere much with arm motion. They are easy to hold onto. I almost don't notice that they are there. And they do just what I wanted - provide hydration on those shorter runs when a fuel belt seems like too much. Definately money well spent. How on earth did I manage before?!?
A few of you have inquired as to which I like better. I'm honestly not really sure. I like them both for different reasons. I prefer the cap on the Nathan model. I also feel that the reflective detail is a nice feature. However, the Amphipod seems to fit my hand better, holds a bit more liquid, and has a pocket that may come in handy sometime.
If you're in the market, you probably won't go wrong with either one!