Try Targus Atmosphere
I've been using a Targus Atmosphere TNT007EU for about 5 years. So good I just bought another off eBay, plus 5 more for other colleagues. You can currently find them for £17.
The description says 15.4" - don't be fooled. My regular laptop is an old 17.1" HP model - full widescreen and not very thin. The case regularly carries the laptop, loads of papers, large assortment of cables, 2 CD wallets, 4 LTO backup tapes and an external DVD drive. There is room in the proper laptop compartment for 2 laptops or maybe 3 if they're thin - and dividers to keep them separate.
The rear compartment expands - it has an all-around zip that allows it to be made larger. Even without doing that I have carried my lunch in there. The pictures show it expanded and holding a printer and that is certainly possible.
The strap is wide and compfortable, although the one time I carried 3 laptops, I wasn't sure I could trust the stitching and metal attachments, so I used the handles - which are also quite good.