I may be pointing out the obvious, but the rules Chris mentions - B'Masao and Rock The Casbah are supplements for I Ain't Been Shot Mum (Company) and/or Troops, Weapons and Tactics (Platoon), while Charlie Don't Surf is a stand alone set. Good rules, using a very similar system. Some folk don't like that a turn can end abruptly and before every unit has been activated. To me this a strength of the rules though as opposed to the plodding 'move everything, shoot everything' sort of games. The games are reliant on 'Big Men' - the force's leaders and good use of your commanders can make a big difference.
Force on Force: Ambush Alley is as good, but different. While you can happily play with the core rules, the supplements like Ambush Valley (Vietnam) and the forthcoming Bush Wars, add more flavour to the basic game, specific to what conflict they cover. The rules use the 3-5 man fire team as the basic unit and work from this up to a company sized unit, although they struggle to give a flowing game once you get to that level imo. Training, Confidence and Morale are the integral factors defining your troops here and the rules don't get too hung up on individual weapons load outs... the man not the weapon is the key factor. Shooting and moving is done by fire team and against fire team. Gaining the initiative in any contact is important and troop quality comes into its own here.
Between the two games I'd be hard pushed to say either is a better set, they're both good at what they do. FoF gets slammed by some people, as some of its mechanisms can be hard to grasp at first and they try to play it like other rules they own, which doesn't work oddly. If you know guys who have them both, why not try out a game with both? See how they fit you for size? I have both and wouldn't be without either... I don't use any other rules for this era and level of game.