The Y&C Gel Xtreme gel ink pen can be found at most stationery and craft stores, as the pen comes in a standard 0.5mm size with black, blue, and a few colored inks as well as in a 0.7mm size for metallics (gold, silver, and bronze were the ones I saw available). What I like is the 0.5mm tip has a needlepoint tip, so I have a line that's wide enough for my taste with a thin tip that gives it a bit more style. I like the barrel as well, a thick, rounded plastic with a comfortable beveled grip area.
The 0.7mm metallics are fun, I don't remember if the above is gold or bronze (I think the latter) but they glide over the paper (Rhodia's Le Carre large pad) and the ink is shiny enough to stand out from the graph lines. The Y&C Gel Xtreme pens are skip-proof, and the $1.39 price is right too.