I used this pattern:
...but I made mine shorter, to just cover the wrists, because I usually wear long sleeves when it's cold enough for wrist warmers.
They came out quite big around. Probably anyone with medium to small hands/forearms who doesn't knit very tightly should make them using a smaller needle. (I used #8 as suggested in the pattern.)
This pattern is based on the Irish Hiking Scarf pattern which is available here. I made a short scarf based on that pattern...half in gray and half in pink-and-maroon stripes. It's a very odd looking thing. I rather like it, but I don't think I would wear it in public :)
The fun thing about this pattern was that I got to learn mattress stitch with the help of the online video at http://www.knittinghelp.com/knitting/basic_techniques/misc.php. Mattress stitch is cool because at the end you pull the strand of yarn and it "zips up" and disappears.