I always planned on an Inquisition element to round out my imperial forces. Being an elite force, I foresee these being quite expensive points wise, so a 1500 - 2000 pt army should come relatively cheaply in £'s.
Initial thoughts for me would be 3 squads of terminators in storm-ravens, with the rest rounded out by troops in power armour and a few dreads.
I'm hoping that there will be Guard in the list too, as I have heard that the allies rule will be a-gonner. So between the Codex: Marines, Codex: IG, the Tyrants Forces list in Badab War pt 1, and the new GK codex, I'll have a fully integrated force. Time will tell, though.
Looks like I'll have to add a new tab to the page, and start saving some pennies...