You might want to consider the Pioneer speakers that get rave reviews. See link below for their center channel speaker. These speakers do have a rear port, so you will want to place them about 8+ inches from the back wall. But I doubt you can do any better for the money, $69 ea.
They also have stand mount and floorstanders from the same lineup, research and determine what will work in your environment...
http://www.google.com/shopping/product/3617682299012118837?lsf=seller:1311674,store:1190912619498917587&hl=en&lsft=ref:212,loc:1&prds=oid:13160185543627251501&sa=X&ei=ML0FVfjcCovFgwSWjYCABQ&ved=0CEIQrhI
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They also have stand mount and floorstanders from the same lineup, research and determine what will work in your environment...
http://www.google.com/shopping/product/3617682299012118837?lsf=seller:1311674,store:1190912619498917587&hl=en&lsft=ref:212,loc:1&prds=oid:13160185543627251501&sa=X&ei=ML0FVfjcCovFgwSWjYCABQ&ved=0CEIQrhI
-RW-