I don't even own the 40k rules yet and I'm already planning what I may buy over the next few months.
Just announced by GW is the new Dark Eldar range and believe me they are looking sweet!
The old range of Dark Eldar never did it for me, I always felt the figures just didn't live up to the horrific and calculated savagery the background material attributed to these vile creatures. The new range however looks to do justice to these twisted brethren of the Craftworld Eldar. Just look at some of these images (swiped from GW.com).
Dark Eldar Reavers
Dark Eldar Kabalite Warriors
Dark Eldar Incubi
For more info head over to Games Workshop Dark Eldar Range