At our annual vendor fair the Staples table was loaded with swap, and among the items they were featuring was this Paper Mate Biodegradable ballpoint pen. The components are made from a corn-based material which, when planted in soil or composted, will degrade within about a year.
First thing for me always is aesthetics: do I like the way it looks? The answer is yes, I love the cream and mint colors. The pen is a bit bigger than I would like barrel-wise and the 1.0mm tip as well. Overall, it looks good, writes well, and is a keeper (until I want to get rid of it, and then I won't be worried about recycling).
Paper Mate's Biodegradable line also features a mechanical pencil, which a friend of mine picked up. That too looks nice and works well, so both are definitely something to think about if you're looking for green office products.