Inspired by this and the default Pidgin look, I hacked up all three files to make an extremely compact theme, with smaller text, and less spacing. I also remove the date from the per-message timestamps, putting Pidgin-style "Conversation on [day]" headers above each day. Further, tapping a timestamp will expand it to show the day as well. I like it, and I put it out here in case other people are interested.

edit: Whoops, forgot some other features and a screenshot. My setup doesn't show the usernames. Instead, it colors the timestamp, so blue is for you, red for the other person (this could be easily changed by editing the html). It also puts space in between long pauses; 5 pixels for a ten minute pause, getting longer as the pause does. You can see this near the top of the screenshot: