C9 lmg, sexy beast of a gun, takes standard 5.56mm 200 round belts, easy to use and clean, pretty solid metal design other than the plastic fore-grip also accepts standard magazines in a special port.
either that or the c6 gpmg...love how that thing sounds plus its metal and wood with 7.62mm rounds.
both were great toys back in the day, but my c9 was my baby, and i didn't let anyone touch her.
edit: just realized this was about games...uh realistic shooters: m4 with a reflex or acog sight and an under-mounted master-key, i cant think of a problem that cant be solved with one of those.
unreal: the ripper, spinning discs of decapitation that bounce off walls and floors if they miss, alt fire to explode on contact.