I realize they are not very common anymore, but I have a South African army field pack that kicks butt. It is capable of carrying more than I can lift.
Extremely heavy duty, as you can imagine. Sheeple friendly brown (very coyote-ish).

I like the mystery ranch 3 day pack.

I need another pack like I need another.... knife, or watch, or pair of boot, or....

I dont have the experience with this exact pack, but I can vouch for Osprey. I have one of their packs and its the only pack I take with me on hikes and overnight camping trips. We dont do too much rucking/hiking when me and my boys go camping mind you, but all things considered you simply cannot beat an Osprey. Im a backpack guru. I love packs. Kinda like knives, you cant have too many IMO. If I had to recommend you a pack, I would say pick from the Osprey line. THey have them for almost any application. Now if we could talk the Army into letting us have an Osprey rucksack, I'd be a little more cool with the 10 mile ruck marches at 0300. <img src="/ubbthreads/images/graemlins/shocked.gif" alt="" />

LOL Thanks Recon..... 0300 road marches..... WTF.... That is why I am in armor!! They say road march and I tell the driver to start the tank!! LOL

if you're looking for a "tactical" or military type pack look into Kifaru, I actually have my EMR for sale right now... You could also look into Tactical Tailor, that is if you like the Alice type pack.
I've heard good things about Mystery Ranch but have never used, they are built tuff.
Lowe Alpine actually makes very strong packs, they will last you a good long while, Mel from Kifaru has a very big one for sale on thier forums,
kifaru

let me know if you're interested in my EMR, it's woodland tri color

I have a Blackhawk 3 day "tactical" pack but it is the last thing I would want to carry on foot for long. It is perfect for car or airline travel though.
What someone said about lots of pockets is dead on. For luggage the Blackhawk is perfect. I also use it for carrying large amounts of grocerys on my motorbike.
It is tough enough to handle heavy items and the drag handle is very good.

I have a a Trekk pack which is ideal for backpacking but horrible as a day pack or luggage because it has just 2 huge pockets that are a pain top open. You can wear it all day though and stuff does not shift. It is also very light even with very padded straps and belt and aluminium frame.

I roll an old army backpack from the 1942 era (thats what's printed on it so it may not be but who knows) i repadded the steel back bars with foam and duck tape. lots of room and comf as hell. and i think its got alot of character.

here is a pic