Unit/Raid Frames and Damage Meters were the top two. I'll look at putting together something for Damage Meters first since it's not quite as huge as Unit/Raid Frames. Here's a list of some of the ones I know about. Please add to it if you see one that you know of or that you are interested in.
Assessment, KTM, Recap, Recount, SWStats, Violation
Also, I am considering some sort of performance measurement if it isn't too time consuming. Any suggestions besides a basic memory consumption monitor during battle at the OS level?
KTM isn't really a damage meter, unless your lumping threat and damage into one, in which case maybe add Omen. As for monitoring performance maybe use Option House or Performance Fu or some other performance monitor. You also have to consider when doing Damage Meters that 2.4 is coming soon so your review will become out of date fairly quickly because of the combat log changes, some mods may die, new ones may be created.