If you are walking a lot, you could try a belt pack
http://www.thinktankphoto.com/categories/camera-beltpacks.aspx
or digital holster with a pro belt (with a couple of modular components)
http://www.thinktankphoto.com/categories/digital-holsters/digital-holsters.aspx
I find this to be much more comfortable than a shoulder bag (but I do have a bum shoulder).
If you are just going to carry single lens (not huge) on a smallish digital camera and want a shoulder bag, the Retrospective 5 is great. The UD35 is really good but holds a ton (so you might end up overloading it).