the Deuter Guide 45+ is meant to be pretty good. My cousin who works as a park ranger for wildlife reserves speaks highly of them. Also, it has an extra 10 litres of space, ontop of the 45 it already has, so its pretty good.
http://www.deuterusa.com/products/productDetail.php?packID=guide45+&sub=alpine&tert=futuraZero
http://www.deuterusa.com/products/productDetail.php?packID=guide45+&sub=alpine&tert=futuraZero