Zotero's reports are very useful, but they are unfortunately a bit inflexible. So, I hacked together a script to give me a little more control. In addition to letting you modify the data included, it also inserts all the styling as inline CSS, so you can send a colleague your pretty report without having to include seperate stylesheet files.
Dec. 2012 update:I'd love to keep adding features on this, but I'm currently working on a PhD and co-founding a startup, and the time just ain't there. However, feel free to fork it on GitHub and hack away; I'm happy to pull in new features, or of course you can just run your own version somewhere.