There is also the
M-ROCKsling bags. The Olympic and Arches. I had a Lowepro Slingshot 100 but I think the M-ROCK Olympic has a better shape. You can fit more in the M-ROCK.
Tenba has an interesting
Shootout sling bag. The video gives a good idea how it can be used. It looks ideal for people with long lenses as you can gut the bag then load straight through the top door.
Sling bags are great but are not suited for every day use. They take a toll on the kneck and shoulder.
The Lowepro Fastpack bags are regular backpacks that have side openings like the slingshot bags. You can use them like a slingshot when shooting but get a more comfortable double strap fit when on the move. I have the Fastpack 100. It is much easier on the neck and shoulders but I hate the shape of it. The top compartment is to big which makes the lower compartment to small. It has a nice size but overall the design should be better.