Pet rocks are way too old school, but not anymore thanks to ThinkGeek's new USB powered pet rock. The rock with a glued-on USB cord will only run you around $10.
I know it would ruin the link to the pet rock, but how about a nice had-warmer version. A nice warm rock to warm the fingers on might be good. Last week it was so cold at work I filled a coke can with hot water just to thaw out my stiff fingers.
james b gives me an idea - just put one of those little 'wifi detection' gadgets on the surface, instead of a cord, and you could have a wifi-detection rock. it's not AS ironic, but at least it'd have a use. (I think using a rock to detect signal strength would be quirky/novel enough. :P )
This will really catch on soon as a bachelor thing to have. Nobody will actually get it (besides history geeks), but its perceived irony will certainly entertain.