The Zebra F-301 is awesome - I keep both blue and black at my desk at all times. Reliable pen, good feel, and eminently affordable. Zebra also makes an F-301 Compact, a non-retractable that's about 4" long, fits in your pocket without poking you, and becomes full length when the cap is put on the back of the pen. Uses the same ink cartridges as the rest of the F-301 line. Every day carry for me w/ a clip of index cards (almost a Hipster PDA, but I don't quite use it like one) and sometimes a small notebook.

I switched to felt-tips a few months ago and will never look back.

Props on the Zebra F301, though I prefer the black ink.

I like http://amzn.to/feb5cC, although it's not as small as a Moleskin notebook.

what about a ruler ?