Probably a Barret chambered for 50 BMG. Just something overly expensive that's more for fun and show than practical use.
That or an FN PS90 which is something I can't afford now but hope to afford in the future. That may have a more practical use than the Barret.
Oo now that I remember the Beretta Billenium I think it was called is a pretty sweet looking piece of metal.