I bought this Ortlieb Compact handlebar bag before going on a week-long bike tour: http://www.rei.com/product/737832. I love it! Big enough, but not too big. Easily carried my camera, wallet, a few other small items. Stiff and stable. Can lock it on the bike, or pop it off in a second. Shoulder strap, too, so you can carry it like a purse when off the bike. Ortlieb has a couple of larger versions, but I didn't want to feel like I had a piece of luggage on my handlebars, LOL!

I bought a plain black version from Wayne at thetouringstore.com. Wasn't listed on his website, but I contacted him and he had several in stock.

While I was at it, I nabbed an Ortlieb underseat bag. The two items together give me plenty of storage on the bike when I need it on long day jaunts.