I'm also an amateur photographer and I've also looked around for a handlebar bag suitable for carrying my Minolta Maxxim and two lenses. I have yet to find one of a suitable size with an appropriate amount of padding. I could only use it on the road bike, but I'd love it if someone out there knows where to find a good one.
For the mountain bike, I'm having a small [censored] pack custom made by a local shop. It's being custom sized to hold the Minolta in it's padded Lowe Alpine bag, a small first aid kit, a snack, a light jacket, and a water bottle on each side. It's going to run me about $70 but it's worth it. Maybe I'll have them custom make a handlebar bag for me too.
For the extremely technical rides, I'll still leave the Minolta home. I'd rather use it than my cheap digital, but I can afford to replace the digital if I crash and burn on top of it.
Bri