I have one of the toploading Lowpro AW holsters. I removed the shoulder-strap and put a heavy-duty web belt on it. Then added lower strap around the bottom (think, military gasmask pouch-on-the-leg.) They don't show it (they always show it on the chest for some reason) but at least on the older models on the backside there's a wide hip-belt slot. I actually use a military web-belt with ALICE clips with the handle loop on the back but both work.
It has the SLR w/tele+hood, all the supplies, an extra 50mm 1.4. Attached to one side is a flash (SB-800) in its case, and on the other I put a drawstring waterbottle holder. Double double duty as water carrier and/or catchall pouch, or secondary flash.
I love it. Mostly I love..
1) It doesn't interfere with the pack, at all
2) It does not bounce around
3) I can drop the camera in, swipe the zipper and have both hands free. In or out takes < 5 seconds.
4) It's comfortable. I've worn it on multiple 12-hour stints.
5) When I go to Disneyland, I have both hands free with no camera in the way. I can put my kids on my shoulders and it's not in the way. They're not kicking it. It can go on rides with me, by shifting it around to the front of my leg.
6) The weight is mostly on your leg
7) When I bend over, the camera doesn't fall in the way.
8) It never shifts around when I raise my arms, tip sideways, or swing when I stumble. Wait, no, I never stumble. IF I stumble. :)
9) Built-in raincover.
10) It makes for an acceptable day-hike carrier. Note the water-bottle carrier above, and depending on what side you get it'll hold various amounts of food, wind jacket, etc. If you're carrying the camera anyways, you can fit a decent amount in there unless you have a monster FF w/2.8 tele on it. Then it gets a little tight.
1) Padded carrier is not silnylon. But at least it's protected!
2) It's a tad heavy, but the stuff's protected!
3) The belt CAN interfere with some backpacks. However, you don't have to worry as much about the positioning of the belt because, since the weight is mostly on your leg with a lower strap, it has a broader "acceptable ride pattern." The belt becomes less load-bearing and more bounce-control.
I looked at the more recent models on Lowepro's website, but it looks like they have changed up the bags.
This is the closest .... http://store.lowepro.com/toploading/toploader-pro-75-aw
Here's the older version that I have:
Regardless, check out that style of case ... I really (REALLY) like having it on my leg.