I'm fine with that, cameos should be recognizable without seriously impacting the original material. Maybe some sort of disc weapon would be cool. Wouldn't mind seeing a light cycle cameo either (dunno how useful that would be, and its not a weapon per se, but it would look fancy. )
Spinfusor Disc launcher? It's the classical weapon of the Tribes franchise. Shoots bright blue highly explosive anti-gravity uranium discs. Single shot then reload.
forgot the exact name but buzzblade gun from rachet and clank shoots out these chainsaw like blades at high speed that bounce and hit multiple enemies
Definitely this one And not to have difficulties in copyright, but the Portal Gun might not be hard to implement.
How about a Portal gun (from the Portal games)... Preferably without actual portals, just an orb that does damage. A Minecraft pixilated bow would be the second ultimate cameo (second to a Creeper into Starbound) Finaly I agree that a HalfLife crowbar would be awesome.
These: Dual Wield, of course! (with attachable Silencers, laser sight, extended magazine, and so on.) Now to find a "Armor Cameo Suggestion" thread and suggest black suit & red tie.