In reply to Easty14:
I wouldn't go for the dmm flight. I've got it and is a great pack but not definitely not for trad climbing.
Often I find myself climbing with the backpack on multipitches or coming out of the crag / cliff. DMM flght is quite bulky and it has no way to reduce the volume.
I use a deuter 30l , very similar to Hagloffs mentioned here... I really recommend it.
Regardless the brand, most important is how it'll fit on your back. Go and try different ones. Most of them are really good and very similar on capabilities. Look for alpine climbing specific backpacks. They are mostly between 30 to 45 litres. You can fit a full rack, and they can still reduce on size that you can climb very comfi with them.
Be sure you'll regret if you have the best backpack but is not comfortable on your back.
Cheers