Checklists and Hierarchies
As I understood from the Google Wave preview, Polly is a centralized poll tool which seemed to only support single votes. However, there are many situations where this is not enough. Checky (checklists) and Ranky (hierarchies) would be cousins of Polly.
In the simplest sense, checklists and hierarchies rely on a centralized set of choices. The pool of options could be dynamic and editable by anyone. The generated results could be static and painlessly inserted into replies. Checklists would benefit from clicking checkboxes. Hierarchies would benefit from a drag-and-drop sorting. However, this isn't very different than what can be accomplished with current tools.
I am not sure how feasible this is, but if extensions have the ability to spawn parent and child versions of itself we could make some improvements to Checky and Ranky. Ideally, a parent would sit at the root wave and unique children would reside in each of the responses. The parent would contain the possible options and aggregate the results (highest item total, lowest item total, etc.). The children would represent personal votes. This allows the pool of options to evolve and refine itself. And it allows users to easily update their results.
One of the more complicated memes I've encountered was a list of books
that required different text styles to signify which ones were read
completely, read partially, read in school, enjoyed, hated, etc. Applying the necessary HTML tags was really better suited for being an automated task. I'm not sure if creating a "keys" for results from complicated dynamic checklists is a sensible feature for Checky, but perhaps it is a feature later down the line.