We use the Cannondale Toot handlebar bag. You can see it here.... http://www.nashbar.com/profile.cfm?c...eid=&pagename=It's fairly small, with a quick release so it's pretty handy for carrying wallets, phones, cameras, snacks, etc. It slides right under the STI cables.

Only thing I had to deal with was the larger bars we have on the tandem as opposed to the single that I used the bag on prior. I had to do some grinding on the plastic mount with my Dremel to make trim away some of the plastic arms so it would fit.