Didn't read your whole thing but my favs are (in no order)
1. AK-47 in any game. The gun is a legend. Its on the flag of Mozambique for fuck sakes!!!!
2. Auger in Resistance. I love puttin up a wall and shooting chimera through it!!
3. Spartan Laser in Halo 3 is cool
4. Golden Gun in any of the Bond games. My favourite bond game is Nightfire and it had the golden gun.
5. The grenade launcher in Killzone. Not the large one, but the pistol one that shoots one at a time and you reload it after each shot.
6. Also from Halo 3 the energy sword, cheap as hell but fun
7. Desert eagle, its been in many games, most notably Call of Duty 4
That sums it up for now. If i think of more i'll re-post