I am no help, I completely missed mine this year. I will be doing something for my upcoming 500th post, but what remains to be seen!Basically, you should do whatever you want, it's your blog:)
I completely missed mine as well... oops. I've seen where others have done an 'overview of the year', just a walk down memory lane of what happened since they started blogging.
I totally missed mine for two years in a row I think! Some people have giveaways... I would maybe do a look back at your favourite posts? A post about why you love to blog, what blogs you love to read, or just celebrate by telling everyone you know to celebrate with you!
Comments satisfy my need for validation. LEAVE ONE!