This is what I use, and I couldn't recommend one enough.
There's a sleeve at the back for up to a 13-inch laptop, where I keep my 12-inch PowerBook or 13-inch MacBook Air. There's a pocket in the front where I keep my wallet, phone, cables, earphones and my iPad mini. An iPad Air would fit easily too. There's a collapsable side compartment where I keep either my camera or laptop charger, and then there's a lot of space for books and other stuff in the middle.