Awesome topic! Achievements! Let's see now...
Possibilities-
Having X number of PL's
Having complete set of papers, maybe excluding Q or K doc, maybe not
Donating X amount of cash (Mur will get richer with this medal.. >)
Doing voting X number of times ( to encourage people to do some work for benefit! )
Exploiting bugs, maybe? Nah, everyone'll start doing it.
These are all I could think of in the few spare minutes I gave typing this... On an iPod. Accursed iPod.