Mountains Plus has several different Camelbak models available right now at 50% off. Here's some of the better deals:
Ruckus .75L Bottle Pack - $37.50: http://store.mpgear.com/camelbakruckus75lbottlepack2008.aspx
Helena Women's Pack - $45: http://store.mpgear.com/camelbak-helena-pack.aspx
Karma .5L Bottle Pack - $27.50: http://store.mpgear.com/camelbakkarma5lbottlepack2008.aspx
Mojo .5L Bottle Pack - $27.50: http://store.mpgear.com/camelbakmojo5lbottlepack2008.aspx
There's others, too. Check it out.