In order of memory:
1. The Everscamp staff (or whatever it was called) in Oblivion. on a good day, it infinitely (re)spawns four scamps on whom to vent your every frustration, including the bad days in which they just don't pop up again very fast, if at all. "Where the fuck were you, you ugly little pricks!?" *BATTLE AXE* They're also good for leveling weapons skills, unarmed, and target spells.
2. The lightsaber in (SW: JKII)Jedi Outcast, especially paired with another one. That is, an enemy jedi/reborn/whatever to duel.
3. The homing saw-blade launcher in Ratchet and Clank, clank in time. Nothing quite like a swarm of flying razor disks cutting up people you don't like, more fun if you turn on the "rainbow projectiles" cheat. (which, by order of fucking stupid that's taken over in the last few years or so, has to be unlocked first. Having to unlock even the useless stuff, what the fuck, games industry?)
4. Gray fox's cowl in Oblivion. As long as you do the secret identity thing right, you can kill and steal as you like with little consequence when you take off the mask, fuck you, psychic patrol.
5. Telekinesis Plasmid in Bioshock. (I think a potion is still an item, no?) It's such fun to fling things around at cannon-like velocities I hardly used guns unless I was running low on EVE or there was nothing to throw.
