Backpacks-for travel?

I am in the market for a backpack to use while traveling in Europe. I have looked at the Dakine-Jewel backpacks, and I love their prints. Are there similar backpacks, perhaps a different brand, or maker? I would love to have something that's around 19-21 inches, since I will be using it as my Carry-on, as well as while walking the cities.

THREE REQUIREMENTS:
1)Great Prints
2)Must be able to lock zippers. (To keep thieving hands out)
3)Needs to be of good size. approx 19-21 inches

How about checking out WalMart? They have some pretty good and durable ones with great prints. I prefer using the rolling carry-on since it's easier to move and handle when you're tired.