I was looking for the same, for my center channel and surrounds. My B&W center weighs some 30 lbs, and I was going to use 40 lbs monitor speakers for the surrounds.
I had to scrap the plan because I couldn't find anything aesthetically pleasing, and also functional. I ended up going with in-wall Paradigm. The center channel is now sitting on the top of the rack instead of being wall mount below my plasma.
For center channel I was going to use Omnimount MWFS series. They have glass shelves, and there is no strap. The speaker would be just sitting on the glass shelf mounted on the frame mounted on a stud. I don't sleep under my plasma, so I don't have to worry too much about securing the speaker.
And for the surround I was going to use something like Omnimount ETV13 or TVM13. They are designed to hold 50 lbs CRT TVs. You'll have to come up with your own strap to secure the speaker on the shelf though.