Firearms

Ebony and Ivory
Location: Dante begins play with these.
Description: Ebony & Ivory are a pair of handguns which are Custom made by Dante. They are semi-automatic, large-caliber firearms capable of firing just as fast as the player can press the button, which can lead to quite a few interesting combos, such as the Juggle.
  
Shotgun
Location: Mission 2, Library 2F, destroy the desk across from the painting.
Description: A side-by-side, sawed-off 12-guage shotgun, designed for use in close-quarters combat. The shotgun packs an amazing punch when used in close to medium range confrontations, and will be your friend through a majority of the game.

Grenade Launcher
Location: Mission 8, the drawbridge control room, check the skeleton
Description: This 40mm revolving-action grenade launcher packs quite a punch at any range. Its advantage over the shotgun is that the shells never lose their destructive power, even at incredibly long ranges. Its disadvantage is the long reload time as Dante compensates for the heavy recoil and pulls the action. This makes the Grenade Launcher not very good for up-close and personal confrontations, but with the right amount of reflexes one can roll out of the enemy’s attacks even while reloading the launcher.

Needle Gun
Location: Mission 12, On the Ghost ships first lower deck near the stairs.
Description: This particular weapon is Dante’s only option for defending himself under water. Upon first glance, the weapon really doesn’t amount to anything, but if aimed correctly, it can destroy a Sin Scissors or the like in one burst of darts. That is more than any other firearm in Dante’s arsenal can account for. The Needle gun is belt-fed, and fires a burst of roughly 6 darts before reloading.

Nightmare-Beta
Location: Mission 21, Complete the puzzle behind the door with the blue glowing shield.
Description: This is a byproduct of an abandoned Underworld weapons research program, The Nightmare-Beta is a handheld version of the Nightmare boss. It can fire small lasers that ricochet around the terrain and do minimal damage. If Dante has the devil trigger gauge to waste, he can expend three DT gauges to charge the Nightmare-Beta to release roughly 7 laser bolts at once.

Devil Arms

Force Edge
Location: Dante begins play with this keepsake.
Description: An ornate and heavy sword that was a keepsake handed down to Dante by his father. This sword has a relatively short range and is decidedly weak, but it does serve its purpose in teaching you the basics of melee combat.

Alastor
Location: Mission 2, protruding out of the woman statue.
Description: This sword is possessed by the demon spirit Alastor. When wielding it, Dante gains access to the Devil Trigger ability. Alastor is a lightning-based spirit that gives Dante extreme speed and high-powered airborne-based moves. The sword also has some of the more useful abilities of the game attached to it, such as Round Trip and Air Hike.

Ifrit
Location: Mission 9, Ascend the floating platforms to gain these.
Description: These strange gauntlets are possessed by the demon spirit Ifrit. When worn, Dante still has access to Devil trigger, only this time it will trigger him into the Ifrit state. Ifrit is a fire-based spirit the grants Dante increased damage and defenses. Ifrit has some of the most powerful abilities of the game, including Rolling Blaze, Meteor, and Inferno. Keep in mind that in wearing Ifrit, you must purchase an ability to gain access to the High Time move again, in which case Dante will knock enemies into the air with an uppercut instead of a sword swipe.
Ifrit allows Dante to perform some of his most spectacular martial arts moves, and one of the better aspects of this is, if you have the time to spare, you can charge up each blow to deliver extra damage.

Sparda
Location: Mission 18, Cut scene.
Sparda is the sword wielded by the Legendary Dark Knight, Sparda, Dante’s father. This sword has several pros and cons, it is a highly damaging weapon with multiple forms, it retains Alastor’s Stinger and Round Trip abilities, and it looks very cool. On the downside, until the end of the game, Sparda has no Devil Trigger whatsoever. And while it does have two of Alastor’s abilities, it does NOT have all of them, most notably, Air Hike will no longer be accessible.
Sparda still is an awesome sight to behold and does pack a major punch, it is not recommended for use in boss fights as the lack of DT makes things difficult, but it is an excellent sword to use on enemies such as the Plasma.