Unreal Tournament 2003
Quake III Arena:
-Urban Terror Mod
-True Combat Mod
Half-Life:
-Counter-Strike Mod
-Natural Selection Mod
-FireArms Mod
-Svenn Coop Mod
Halflife is still a lot of fun due to the amount of mods people have created for it. True Combat and Urban Terror for Quake III Arena are a lot of fun and more realistic than Counter-Strike. Well, True Combat is anyway. You can even aim with the iron sights on any weapon, including pistols. If it has a scope then you can use it, which also includes real-to-life lense effects on the sight. See it for yourself:
Of course, that screen isn't from the latest version, either.
Same for that shot, but it shows a cool nightvision scope.
And now to reassure you that the models don't suck, here's some screen shots of the revamped beta 1 models (vs beta .45 like I used to play):
Iron Sights on the M4A1: