I was looking at the new releases on the GW site today and noticed a few models in the new Vampire Count releases that'd make for some interesting conversion possibilities.
The Isabella Von Carstein model would make a great Lady Malys with a head and weapon swaps, and I think she's posed a little more dynamically than the DE Lhamian. (Would also be good for a female Sliscus/Vect/etc.).
The Crypt Horrors from the Vargheist/Crypt Horror boxed set look like they'd make pretty decent Grotesques with some added leftover bits that I'm sure most of us have lying around. It's not much cheaper than buying 3 Grots, but they have different poses and are plastic. I think I'm actually gonna do this so I'll put up pics when I get a chance (they also look like they'd make solid Clawed Fiends more or less as is, but I don't think anyone actually uses those haha)
The Coven Throne/Mortis Engine look like it has some interesting bits for making a Dais of Destruction as well, but it's a pretty expensive kit so thats definitely one to wait for till the bits start to hit Ebay.
If anyone else has any cool conversion ideas to add, feel free.