Without spending a fortune I can recommend the OMM adventurellight 20 and last drop 10. The good and bad bits....
Both are really light material so weigh less than many other brand smaller packs. 10 is a great training runaround, but I've used it for ultra's before. The 20 has more padded straps and two pockets on waist strap for easy access, the angled mesh pockets are great too as you can get two bottles in them and retrieve easily on the move. I'm a convert to the ease of bottles rather than faffing refilling hydration packs and never knowing how much liquid I have left, so the bottle carriage is important to me. The raidlight packs with front bottle holders look good to me, but expensive and from trying on the OMM pack I find bottles attached to front straps bounce too much (maybe just the OMM system?) and its nice to have them out of the way, accessible just above waist height.
The 20 can also be compressed down quite a bit so it fills the capacity gap between 20 and 10L packs well for me. Despite less features I love the 10, compact and sits tight to your back (neither bounce, unlike many ultra runner's packs I see - that would drive me mad over several hours), also has side meshes which bottles can go in, but due to size of pack these aren't angled so not as easy to withdraw bottles while still running.
Never had 'rubbing' problems I can recall and the 20 has seen me around a 100 and several 50+'s. never filled the 20 other than when doing Coast 2 Coast and nearly did on Fellsman where there's a strict kitlist and I've downsized my gear since then.
Though have to say that Saloman pack Squeakz recoomended looks really good. Does the price reflect the innovation? Does the mesh vest bit cause the chest to heat up any more than with a standard vertical strap pack.
Edited: 08/08/2011 at 17:14