I just keep buying MB sets on clearance like a fool, but I've only built about half of them.
Every saturday, my 9-year-old son just wanders into my toy closet, pulls out a new set, and builds something. He doesn't really care about military stuff, but he has the most awesomely random CoD, Halo, Halo-cop, astronaut battles.
Found some halo sets on clearance over the weekend, so hopefully they can integrate into the CoD stuff. I don't give two shakes about Halo or their figures, but the Firebase and the UNSC Countdown look like great HQ set pieces. Can't wait for the Pelican Air Base to get cheap too.