In reply to chmckay:
I recently bought an Osprey Mutant 28 for exactly that purpose. I think it's perfect for scrambling and multipitch days. You can fit a lot in it, especially if you pack carefully and utilise the rope strap and/or helmet holder on top and it copes well with heavy loads. When you don't need to carry as much, it easily compresses down really tight whilst retaining a good shape and the hip belt clips away quickly around the back for climbing.
I've comfortably carried double 50m ropes, a decent trad rack, harness, shoes, helmet, drink, food and some small layers. But when we got to the climbing it compressed down well and stayed out of the way. Basically, it's really versatile.