First off, stick with what works (or at least, what works for me). As I wrote in “When did you first take part in RPGaDay?”, I enjoyed RPGaDay the most when it used question-based prompts, rather than one-word topics.
Beyond that … I don’t know. Maybe a video channel on Youtube that pulls together people’s different video contributions? Organize some online games amongst RPGaDay participants? It’s hard to say because, unfortunately, I just haven’t been paying attention to what other folks have been doing. That said, I do want to go back and see what other folks did this year, so maybe I’ll have some other, better ideas after that.
As for what I would like to do next year, I’d like to mix it up a bit. Other folks do videos; that might be fun to try. A podcast-a-day contribution, published on the Nuketown feed, could also be interesting. Both require more work and forethought than your average blog post, but I like the idea of branching out.