Certainly one of the greatest innovations of the Megaman games is the ability to copy the weapons of the Robot Masters that Megaman defeats. Once aquired, these weapons are yours for the rest of the game. However, they run off weapon energy, which must be replenished by collecting special capsules. In order to refill the weapons energy, you usually have to equip the weapon first. However, most of the later games have a special item called the Energy Balancer. If you have it, you can pick up energy capsules with just the normal buster equipped to automatically refill the weapon with the lowest energy. Here is a complete database of the various weapons Megaman can aquire throughout the games.
Air Shooter
Astro Crush
Atomic Fire
Ballade Cracker
Bit Cannon
Black Hole
Blade Launcher
Blizzard Attack
Break Dash
Bubble Bomb
Bubble Lead
Centaur Arrow
Centaur Flash
Charge Kick
Copy Vision
Crash Bomb
Crystal Eye
Danger Wrap
Deep Digger
Dive Missile
Drill Bomb
Dust Crusher
Electric Shock
Fire Storm
Flame Blast
Flame Sword
Flash Bomb
Flash Stopper
Force Field
Freeze Cracker
Gemini Laser
Grab Buster
Gravity Hold
Gyro Attack
Hard Knuckle
Homing Sniper
Hyper Bomb
Ice Slasher
Ice Wall
Ice Wave
Junk Shield
Knight Chain
Leaf Shield
Lightning Bolt
Magic Card
Magnet Missile
Mega Ball
Metal Blade
Mirror Buster
Napalm Bomb
Needle Cannon
Noise Crush
Nuclear Detonator
Oil Stream
Pharaoh Shot
Pharaoh Wave
Photon Missile
Plant Barrier
Power Stone
Quick Boomerang
Rain Flush
Remote Mine
Ring Boomerang
Rolling Cutter
Sakugarne
Salt Water
Scorch Wheel
Screw Crusher
Search Snake
Shadow Blade
Shark Boomerang
Silver Tomahawk
Skull Barrier
Slash Claw
Sonic Wave
Spark Chaser
Spark Shock
Spread Drill
Star Crash
Super Arm
Tengu Blade
Thunder Beam
Thunder Bolt
Thunder Claw
Time Stopper
Top Spin
Torch Arm
Tornado Hold
Water Balloon
Water Shooter
Water Wave
Wave Burner
Wild Coil
Wind Storm
Yamato Spear