Check out the Magnepan MMG-W speakers......very creative solution, and perfect for wall mounted plasma displays. They are also very inexpensive ($299 pair).
I recently installed the Artison Portrait LCRs, they solved my problem of finding a way to hide the center. They're expensive but were cheaper than some of the other options I looked into.
These have high WAF, but sound better than any other plasma speakers I have auditioned...well, except for the Martin Logan Fresco. The Fresco's did not "look" right, didn't fit with the decor.