+1 on Kelty Map 3500. I own and use two. One for a BOB, and one for deployments, travel (including carry-on), big day/overnights, etc. Here's the Kelty as my BOB setup.

Here's my previously posted review:
This one is worth a look. The big advantage is a real, functional, internal frame that transfers the load to the hips efficiently, meaning you can carry serious weight comfortably, if need be. However, it's volume is more like a large day pack. It is also very adjustable for size. It doesn't look too "tactical" and blends in like an ordinary day pack, especially the "civilian" colors. It's $100 with free shipping, which may be over budget, but it is listed elsewhere at over $170, and well worth it. I own two; one is for deployments, the other is my BOB/travel/day hiking pack, and I'm very happy with them after extended use. Kelty MAP 3500

* 1950 cubic inch volume
* 420d HD nylon Oxford mesh cover on back panel and shoulder strap
* 420 gram, 100% nylon Airmesh EVA foam in back panel and shoulder straps
* 500 denier nylon Kodra (1000d on ACU color!) construction, double stitched
* Internal suspension, two fit to form Light-Beam stay rods
* Panel loading pack, single large compartment 2 exterior zippered pockets
* Interior hydration pouch, supports up to 100 oz. bladder, 210d nylon ripstop
* Hydration port at top of pack allows for drink tube to be used over either shoulder.
* Hydration port has snap on top flap closure
* Exterior cargo pocket with fleece eyewear pocket and admin organizer pocket
* Side mesh pockets (fits 1 quart lexan water bottles each side)
* Waist belt (removable) with Scherer cinch system, with waist belt tuck-away feature
* Adjustable sternum strap
* Fully adjustable (removable/replaceable) shoulder straps