I read this thing about Achievements at Digital Orc. If Project NEMESIS still existed, I'd link to one of their posts on the subject. As it stands, I've thought about doing this, either with an XP reward attached or with just a "Hey, you're awesome!" thing (once, long ago, I gave out roleplaying awards to my group, which bears similarities to the latter incentive). The Project NEMESIS post suggested having some Achievements peculiar to the character. So, Urnorn the Wizard might have "kill ten dudes with one fireball" as an Achievement, Two-Hands the Rogue might have "steal the king's underpants during court" as an Achievement, and Grimface the Space Marine might have "punch a starship in half with a fully-charged Power Fist" as an Achievement.
Also, since I was talking about Isle of the Unknown, there's a neat idea about how to tie the hexes together at Monsters and Manuals. You can either randomly pair them together with the first method, or randomize the pairing process so that it can be used on the fly with the second method.