Here's a good deal I found out about thanks to Scott from Weekly Photo Tips.
If you're in need of a good camera backpack with lots of space, the Lowepro FastPack 350 is a good one to consider, and you can get it for $75 right now instead of $125! Using this code on that page will reduce the listed price of $125 to $75.
This offer expires on June 30, so if you're thinking about making use of it, you'd better do it right away.
The amount of savings is pretty good, but if you're wondering about the bag itself, here are a few things about it (I've had the bag for some time now and take it with me nearly everywhere):
1) I was able to fit a Canon 5D MkII with battery grip and 24-105 f/4L attached into the main compartment, and although it fit quite snugly because the battery grip makes the DSLR body much taller, it worked fine and I was still able to fit some other lenses in the bag, such as the 24-105 and 50 f/1.4. When I attached the 70-200 f/4L to the MkII, I had to rearrange the velcro dividers to make more room for the telephoto lens, but I was able to fit at least two smaller lenses next to that one.
With something small like my Rebel XS and EF-S 10-22, 55-250, or the "fat pancake" 35 f/2 attached, there's plenty of room for the camera as well as between 3 and 5 small or medium-sized lenses.
2) Yes, the bag isn't very small, so it does take up more space than a bag that will just hold a camera body and a lens or two, but that's because this bag does have a lot more space.
3) The shoulder straps are padded and pretty comfortable.
4) There's a space for a 17" laptop in the back, although I've heard it's a fairly tight squeeze with one of that size - my 11" netbook (I forget the exact size, but it's probably around there, anyway) naturally fits quite easily.
5) There are a few other pockets that I use to stash my 10-22's lens bag (which I no longer use because the lens now fits in my bag, unlike when I used an old Sony camcorder case bag) and various other things such as my wired shutter release. And there are a couple of little SD card pockets as well.
You can see a not-very-clear photo of the bag in my photo, here (it's the one on the right):
Here's Scott's post where I got this from: I got me a new camera bag...