I used this bag on my supported tour in Maryland in May:
Detours Shuttle
Scroll down and it gives you the dimensions--I think it's 7 or 8 inches wide. A nice thing about this bag is that the front flap flips backward to reveal a clear pocket for your map or cue sheet. There's a loop on the flap so you can secure it in that flipped-back position if you want to. Even on an organized, supported tour, you'll need a map or cue sheet for each day's ride.

The bag, though it's water-resistant and has waterproof zippers, comes with a rain cover, and strap to turn it into a shoulder bag when you're off the bike. The mounting bracket stays on your bike.

A little smaller item that I use for short rides close to home is the Adventure Cycling Piggy Pack by Madden. It holds cell phone, keys, snack, some cash, lip gloss, and could probably accomodate a small camera as well. It also comes with a clear pocket for a map, and attaches simply with velcro straps. I just checked the Adventure Cycling site and it looks like they're out of them but you might be able to Google around and find one.

I find that it's true that you want to limit what you carry in a handlebar bag because it can adversely affect steering. But if you're judicious about it, you'll be OK. Definitely get your back asap so you have a little time to get used to it.