4. VC5 Arc Rifle - Killzone 2
A most obscure gun, only used at one point in the campaign of Killzone 2. This however, doesn't make it any less awesome. In unscientific terms, it has the ability to draw in surrounding air and turn it in to electrically charged shots, each with the capacity to kill x amount of enemies stupid enough to oppose me. If you gave this gun to me in any game, i'd become king of that given universe. Sadly enough, it will probably not be known by many people outside Killzone fans. At least I got my fill when I could.
5. Golden Gun - 007 Goldeneye
One of the most symbolic guns in gaming history, largely down to the fact it's from James Bond. Also, did I mention it's completely, entirely Gold. Except from it's cool appearance - you'd look a Don if you walked in a casino with that thing - it too is a pretty good weapon to use. Goldeneye was all about the headshots, and this little beauty provided them.