We've wall mounted many Ikea Torsby table tops (53 1/8x33 1/2") and really enjoyed the streamlined look and hassle free cleaning. Best whiteboards I've ever used. There's actually a white backing behind the glass so everything is easy to read.

For $80 it's much more affordable than actual whiteboards while clearly outperforming cheaper alternatives.

http://www.ikea.com/us/en/catalog/products/90154644/