LaTeX – A document preparation system

Something on the unusual side, but which could emphasize your writing skills or add some "geek" flavor, layout your resume in LaTeX. Then, add it to your skill matrix. Not only will it make your resume a professional, typeset document, but it emphasizes your creativity and technological curiosity.

Edited to add: Not only useful for the interview, but also as a job skill, can't tell how many times I have relied on LaTeX for documentation purposes.