Awards
I like the small badge awards that are given out. I'm sure I'm not the only one who searched through the posts looking for something, anything to comment on to get those last few posts needed to hit 500!
You could give annual award for categories like: Most posts, Most voted up post, most blog posts, most blog comments, etc.
I know it involves more work and I wouldn't want to make a suggestion that cut into your super fun video chatting time @Joshua Dorkin and @Brandon Turner.