I love my space pen! I don't know how generally available the refills are, but my local Office Depot carries them. I have the regular bullet pen. I do a lot of fieldwork, so I like having something I can shove in my pocket, and that will write in all conditions. My favorite all-time pen, though, is the uniball Deluxe micro -- unfortunately, they aren't sold by the box in office supply stores anymore (that I've been able to find, anyway) -- but they're archival, waterproof, fadeproof ink, and have a finer line than their supposed equivalent (vision elite). I haven't tried them on my moleskines, though, so I don't know if there's bleed-through. My 2 (I miss the cent-key ... sigh). Happy writing!