Get one that will take all of your gear PLUS another one of your biggest lens. Then you won't have to shuffle lenses around to put the camera away no matter which lens you have on it.
I would go with a Kata backpack....i have the R103 and it is wonderful. Your stuff might get a little tight...u might get betterresponses in General Gear forum.
I have a Lowepro PhotoTrekker. It's an awesome backpack, airplane legal (fits even under the seat of small regional jets), and fits a 15" Powerbook *perfectly*.