8. Masamune (Chrono Trigger)
Masamune was a chore to get in the game - you had to fight two weird-looking elf-creatures and go on a time-traveling scavenger hunt, and even then, only Frog could use it. Was it worth it? Oh hell yes. Suddenly you have a weapon that's super-effective against evil wizard extraordinaire Magus, and Frog becomes a useful part of your party, instead of the noble but worthless and lazily-named amphibi-man. Really, the only way they could've gotten lazier with a character is naming the main character "Crono" and a robot "Robo." Oh...right. Nevermind.
7. Lightsaber (Jedi Knight series)
A lightsaber is only as awesome as the one wielding it. That's why - despite having ninety spinning laserswords - General Grievous remains a pretty forgettable villain, while Darth Vader remains the galaxy's greatest asthmatic badass. However, a sword made of pure energy does have a lot of potential, and the ones used by Kyle Katarn (part-time Jedi/all-time badass) were always spectacular (and within reason, before the way over-the-top Force Unleashed games). You could slice through stormtroopers, droids, and everything in-between - and, in the meantime, completely forget that there were other weapons in the game. Why would you ever use a blaster? Why would the programmers even bother putting them in? A mystery, that is.