I've recently turned my attention to Necrons until the new DE codex drops. The Necrons will have a new book of their own before too long, although their current rules have fared quite well in 7th edition thus far.
Rumors of the new Dark Eldar are ramping up and I for one can't wait to see what's in store for their release! At this point, there isn't a whole lot of consistency across the rumors I've seen and most seem like educated guesses based on the treatment of Grey Knights and other recent codex updates. Here are some of my un-educated guesses and hopes for the new book.