I've actually researched a couple of sling packs (not specifically for the iPad, though) which included the Incase sling pack.
I was able to see and handled the silver-and-blue Incase sling pack in the local Apple store, and I thought it was (i) quite expensive and (ii) the overly shimmery quality of the silver nylon looked a bit bling/cheap. Quite possibly the material for a different colour might not be so ostentatious, but the silver was just too much for me.
Brenthaven used to make a Titanium series sling pack, although I think it's a discontinued product, I'm not sure if many vendors may still carry it. (It's not on Brenthaven's homepage anymore.) I did see a pretty good review for it on Cnet, but it didn't "get" me, either.
The one I ultimately bought was a Maxpedition Monsoon Gearslinger (on
Amazon at
Amazon.com: Maxpedition Monsoon Gearslinger: Sports & Outdoors). It's manufactured by vendor of hunting supplies, so it's very heavy-duty. But I didn't get it specifically as an iPad accessory - more of a camping/hiking bag. I love it and it suits my requirements perfectly (and maybe just a bit too big just for an iPad and some things.)