I've been happy using the Kensington Contour Pro 17" for my 17" HP ZD7000. It's a bit on the large side (as are my computer and its power brick) but I find it very easy to use and organize with room for everything.

Here's a review with some photos:
http://www.notebookreview.com/default.asp?newsID=2451

It won't fit overhead on a regional jet, but I've had it stuffed with two laptops, peripherals, file folders, and other items and it did fit under the seat in front of me with just enough room for my feet beside it.

$50 doesn't seem like much for a large notebook computer bag compared to many I've seen -- they tend to be expensive!