We use a Jansport one that has been great. We purchased it for our first trip and have used it on everyone since. It has multiple pockets which is great and it has a laptop pocket inside one of the larger pockets which we always use to hold the kids autograph books so they won't get damaged from anything else being pulled in and out of the backpack. It has nice padded straps which is another plus. I'm not sure of the name of the specific one we have but I would recommend that brand since they seem to last.
I'm using my ds's that I purchased at Pottery Barn Kids. It's large and has lots of pockets and storage. And wide straps that fit comfortable on the shouldes.
I just got the Vera Bradley Disney backpack from Disneystore.com I got the black one, the other choice is a bright pink. It's very nice, not too big and not too small. Lots of pockets and very lightweight.
I'm using my ds's that I purchased at Pottery Barn Kids. It's large and has lots of pockets and storage. And wide straps that fit comfortable on the shouldes.