I love my North Face Recon backpack.

According to the user reviews at the above link, most of the purchasers are students so it won't stand out like a tactical backpack.

The pack is well built and has lots of pockets and adjustments. I just recently discovered that it even has a whistle built into the chest strap buckle. Another unique feature is reflective strips on the back.

Specs:
Average weight: 2 lbs 8 oz (1135 g)
Fabric: 420D nylon, 1680D ballistics nylon
Volume: 1830 in³ (30 liters)
Dimensions: 18.5 in. x 13 in. x 8 in. (48 cm x 34.5 cm x 20 cm)

I have been using backpacks for over 40 years and this is the best one I have owned. I have had it for about a year and I carry it 3-5 times a week. It is my BOB.

I got mine at Sports Authority.