My current side deck for my Red-Eyes deck:

Mobius The Frost Monarch (anti-stall)
Lesser Fiend (removes exodia's searchers, morphs into Fiend Skull Dragon)
Cannon Soldier (since I run Inferno Fire Blast, I may want to add to the burn, works with Sangan, Scapegoats)
Cannon Soldier
Cannon Soldier
Mystic Swordsman LV2 (aanti-flips)
Mask of Darkness (trap recursion)
Mask of Darkness
Mask of Darkness
Stealth Bird (adds to burn)
Des Lacooda (extra draw, works mostly against stall)
Magician of Faith (spell recursion)
Magician of Faith
Scapegoat (stall, Cannon Soldier combo)
Scapegoat

My Current Side deck:
8 Monsters
2 Kinetic Soldier (Chaos Warrior)
Blade Knight ( He's so versatile and searchable)
Spear Dragon (scapegoat)
Des lacoonda ( stall decks, increase my drawing power)
Mataza The Zapper ( awesome)
Chiron ( played him befoe he came out )
Zombyra the dark( gets over Vlord and Bserk Gorilla)

3 Magic:
2 Giant Trunade ( DUH!!!)
1 Wave Motion cannon ( beats stall)

4 Traps:

2 Chain Burst ( Get it off before solemn judgement, and you beat last turn)
Curse of anubis ( tech against any kind of effect monsters)
Phoenix wing Wind Blast ( the spin mechanic of this card makes it good against anything)

Theres my side deck and all my reasons, thats a GOOD sidedeck and I DO use it after EVERY game