The two getting on my nerves right now are the inability to distinguish between infer and imply (and I just heard Sam Waterston's character on L&O use infer where he should have used imply ), and compliment and complement.
Complement has various meanings including to complete, quantity required to make up a whole (ie. the full complement of spices), or a colour on the other side of the spectrum.
A compliment is giving props, ie. "that scarf really complements the outfit".