In reply to GarethSL:
> Blue Ice Warthog (26litre)
Their Yeti bags are really good too - just the bits you need, and a floating lid as well (I think) for overstuffing.
Alternatively the Arcteryx Cierzo 35 is good. Not quite as hardy as the Blue Ice bags, but lighter, and fits enough for a day on the mountain. Would be even better with a floating lid, but it generally does okay if you pack thoughtfully.