Today's Wall Street Journal (subscription required) rates five laptop backpacks. The Journal's Overall Favorite and Best Value pick: eBags' Downloader Laptop Backpack ($45). "Tons of storage space without being bulky," said one of the Journal's testers, of the eBags backpack.
I'll add one laptop backpack for your consideration: Codi's new Sling-Pak. The black bag with red accents borrows a bit of its design look from Tumi. And at $148 it's expensive. But I've been using the bag for several weeks now, and I like its compact size, multiple pockets, asymmetrical design touches, and built-in padded laptop compartment.