The blue SLR Gadget Bag for the Digital Rebel Series of Cameras from Canon is a reasonably-priced monster of a bag. It's large enough for a pro but also large enough for an amateur to grow with. The bag is rated to hold two DSLR bodies, three lenses and a ton of accessories.
The exterior is water-repellent making it a bag you can use in all kinds of weather. The large front flap helps to ward off any water that falls on top. Strong quick-release front buckles keep the bag shut but are easy to access when you need your gear. The sides are supplied with two large zippered pockets that will hold accessories - lightmeter, filters, memory cards, batteries, cleaning cloth, iPhone or your MP3 player.
Inside, there are padded and adjustable dividers that allow you to sculpt the guts to suit whatever gear you have. The shoulder strap is wide, padded and fully adjustable. In addition, there are tripod straps so you'll be able to make those long exposure or macro images.