Alrighty, I had a nice list of eleven (or so) potentials that I was looking at, and Ive managed to gut it down to three. Gonna talk through them, maybe give myself reason to pick one over the others.
Black Legion Chaos Marines - These guys are in the lead right now, for the main reasons that I have a ton of them, and they are mostly painted. Any money I throw at them is going to go into the more fun to paint models, and tanks.
Imperial Guard - Ive also got a significant amount of Cadians, though only a few of them are even in the color scheme I want. There is also a lot of stuff Ill need to pick up, like tanks and psykers and more troops.
Empire - I actually dont own any Empire models right now, but Ive been toying with an idea for a Reikland/Altdorf themed force for a good while now. One of the biggest reasons they are on the list however, is that I am going to Midieval Times this weekend with the wife and inlaws, and I know thats going to inspire me to do something with horses...
Right now, the Cadians are taking up the desktop real estate, but Im thinking of swapping them out with the Black Legion when I get home.