I really like
Crumpler bags for between home and office (short trips) and
Techair or
Airbag (same maker) for trips abroad...for the extra protection and for swallowing all my bits and gadgets. I have a back-pack style Airbag which has been lugged around the world on planes and road trips stuffed to the gills and it's like new. It has some neat features like a top pocket with a rubber slot for headphones...many an hour spent with my iPod safely in the top pocket with the 'phones unobtrusively running out the top.
I've had a few laptop bags in my time and these are the most solidly made I have found so far.
Of course if you are feeling rich today you could go for
Tumi, which are made from ballistic nylon and could be said to be the ultimate in bags.
J'bm