To protect the Nikon D90 and allow me to maintain my sanity while commuting with my computer equipment as well, I bought a black and grey Crumpler Sinking Barge bag, which holds a 15" laptop like a Macbook Pro (not the 17" version, though), an SLR and medium-sized lens, one extra lens, and has enough room for a flash, cables and so on. Today I am carrying all that plus a change of clothes.
Crumpler has a zany flash-based website that you just have to experience. It is like a big vending machine, complete with some funny off-color product demonstration vids featuring employees. Good stuff.
What I like about it is that it looks smooth, not like your typical camera bag, has excellent zippers and workmanship, and protects my usual equipment quite well. If I have any criticism, it is that some of the pockets are a little tight to insert a hand, there is no place for a monopod to be clipped (you need to get the bigger Crumpler models for that), and the inside flap is overly long. Overall, it's perfect for my needs.