The Zebra G-301 gel ink retractable has one of the better designs among re-usable pens that I've seen, all black rubber and stainless steel with a substantial clip that won't snap off or get tangled up in fabric. It's a spare, modern look that works well in the office (with the grown ups) or on your own just doodling.
The medium gel ink retractable has a 0.7mm tip that seems a bit wider to me than others I've used. On blank paper it would be fine, but with smaller line widths or gridded paper it might seem too large for writing within the space alotted.
Whatever else, the Zebra G-301 is a great addition to the pen line up: reliable, readable, and comfortable.