Some great daypacks list already. These days, a guy can get a really good daypack for under 5lbs without sacrificing quality & durability. Here is a list of some others including specs.
Eberlestock X2 pack - 1800 cu in 4.5 lbs - one size fits all - super tough frame capable of hauling heavy loads, very modular
Badlands Diablo pack - 1900 cu in 3.1 lbs - one size fits all - awesome breathable suspension, very lightweight but comfortable
Badlands 2200 pack - 2250 cu in 5.25 lbs - one size fits all - great pack capable of hauling heavy loads, better for longer torsos
Easton Pickup Pack - 3000 cu in 4.6 lbs - Adj harness, lightweight and great capacity but still feels like a day pack. has a great hauling capability but is brand new for this year so it hasnt been in the field long.
Sitka Flash 20 pack - 2000 cu in 4.55 lbs - one size fits all - super technical pack, all the bells and whistles, very comfortable.
Tenzing TZ 2220 pack - 2228 cu in 4lbs - one size fits all - good durable pack, simple design
[video=youtube;sFTDpvxu5tA]http://www.youtube.com/watch?v=sFTDpvxu5tA[/video]
Hope this helps!