I'll second the Fisher Space Pen, the Bullet model. I am EDC'ing one in my front pants pocket right now.

Unlike some other mini pen designs, I like that the Space Pen turns into a full size pen when you stick the cap on the end of the pen, so you can actually do a lot of writing with it, if you want.

Debating whether I will get a clip for it. You'd think they could throw in a clip when you buy one.