Cid's Ultimate Weapon

Venus Gospel is Cid's ultimate weapon. This is a very cool looking spear with a huge head. You can get it after you have crashed the rocket into Meteor. Talk to the old man outside the Item Shop, the one who's so obssessed with the rocket. If you talk to him three times, he'll give you Venus Gospel.

Cid's Level 4 Limit Break

You can attempt to get Cid's Level 4 Limit Break, Highwind, after you have stolen a Shinra submarine. In the ocean, off the coast of the Gold Saucer, there is a curious looking crashed ship. Drive into it to enter the Crashed Gelnika. Walk through the doorway at the end of the hall, where you'll find Reno and Rude (unless you have already beat them and Elena in Midgar). After defeating them, you'll gain access to the cargo bay. On the lower level you can pick up Highwind from a treasure chest.