I own a Nikon D60 with 18-200 lens and just cannot find a compact tight fitting carrying case that would handle my Macbook Air, my camera, and basic accessories.
Lowepros are the only ones I know of that also carry a laptop, but they aren't exactly compact - they're sized to handle a 17" (iirc) full-size notebook.
Tamrac has a full line that do laptops, too, with different sizes for different laptops. I have the Adventure 9 and like it well enough, though the "day pack" part on the top is not really super useful for a day pack; I often use it for chargers or my toiletries kit or something similar. I do like the padded straps on it.
You will find plenty to choose from in the Tamrac line. http://tamrac.com/
Be sure that you notebook fits before settling on a particular model of bag.
Personally, I am using a LowePro CompuDaypack. It fit under airline seat, holds my p&S, one DSLR with zoom attached, accessories; 15.4" notebook.
I like their urban disguise line. I've always hated camera bags because they look like camera bags and scream "steal me". Now to get them to get together with Pac-Safe!
I really liked the Lowepro Slingshot. This is a single strap over the shoulder design. The Slingshot 100 was too small so I bought a Slingshot 200. It fit a Nikon DSLR with an extra lens and SB800 flash great.
To include a Macbook Air, may be the Slingshot 300 or 350 can do it.
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