I have been using a Lowepro Flipside 300 for a couple of years now. I can fit the body with a lens attached, my 430 EX, my 50mm 1.4, my 100 mm Macro, battery charger and spare battery, plus five or six filters. On the side pockets I carry spare batteries for the flash, there is a compartment for spare CF cards and other little items. You can modify the interior by moving around the velco attached separators; when I purchased my 70-200mm f4 IS I can leave that attached to the body and still fit it into the bag. Another great feature is that the bag zips from the rear, so when you're carrying it around on your back it has to be taken off before it can be opened - prevents thiefs from getting into your pack.