XCOM would be cool! It's really tailor-made for a ground-level (not command) game, and the latest in the series, Aftermath (still in development) is apparently focused not on XCOM at all but on some survivors after the world gets conquered by aliens, and they have to run around getting weapons, surviving, researching alien tech and the like.
That sounds pretty good for a campaign to me.
Just for the record, XCOM games are (so far as I know) strictly PC (or Amiga), possibly because of their focus on micromanagement. I still remember getting annoyed in the first game when Nigeria cut its funding... they'd been subverted by a nearby alien base, but eh... happy days.
Now for my contribution, I'd enjoy Alice (by American McGee, film possibly by Wes Craven forthcoming). That was sooo twisted, and the weapons were cool. Jack-in-the-boxes with a pyromanic twist, a vorpal blade as your primary weapon... wait, that's not really d20 Modern territory. Instead, what about
Uplink? It'd require a bit of tweaking to both the setting and the rules set, but that game was mad fun.