Now, I get to sit down and write a guide to how the above builds are not only useful, but viable builds that prove that Teemo isn't just a feeding mouse that is useless on all teams.

Runes:
Greater Mark of Magic Penetration - Magic Pen, is used to get the most out of the magic on hit effects also known as procs.

Greater Seal of Evasion - Dodge, Helps against attackers, sometimes Blinding Dart just isn't enough.

Greater Glyph of Magic Resist / Greater Quintessence of Magic Resist - Since we have a slight edge against attackers, Why not counter the Magic Damage we will be taking.

Items:

Amplifying Tome / Health Potion - Allow for early AP and survivability for harassing.

Malady - Since we already have Amplifying Tome Malady becomes the 1st item on our proc item list.

Madred's Razors - Helps for last shotting minions and adds a little damage and armor.

Berserker's Greaves / Sorcerer's Shoes / Ninja Tabi - Recommended for Attackspeed, Magic Pen, or Dodge.

Zeke's Harbinger - If you do not absolutely need the others 1st, or NEED lifesteal.

Wit's End - If facing mana users that are dependent on mana to be affective. ex. Shaco Kassadin Sona Sion. WARNING, If facing these champions also recommend working in a Banshee's Veil possibly replace starks with it.

Sword of the Divine - If you are being Heavily Focused and would like to focus your time on killing turrets quicker.

And last but certainly not least.
Black Cleaver - Amazing item, Can replace Malady or Boots, pending on which one isn't already helping you win the game.

Runes:
Greater Mark of Desolation - Armor Pen, Great for any attacker.

Greater Seal of Attack Speed / Greater Glyph of Attack Speed - More attackspeed, as the build itself will not put you at 2.5 attackspeed.

Greater Quintessence of Desolation - Armor Pen, explained.

Items:

Long Sword / Health Potion - Allow for early Damage and survivability for harassing.

Madred's Razors - Since we already have Long Sword Madreds becomes the 1st item on our list. Helps for last shotting minions and adds a little damage and armor.

Berserker's Greaves - Recommended for Attackspeed.

Phage - One slow proc from this baby and a kill is as good as dead when running away.

The Brutalizer - Used for Youmuu's Ghostblade also early damage and Armor Pen.

Madred's Bloodrazor - If facing a high life team with decent damage out put, ex. Dr. Mundo Vladimir

Frozen Mallet - Nice Slows and Health.
And last but certainly not least.

Black Cleaver - Amazing item, Can replace Malady or Boots, pending on which one isn't already helping you win the game.

Runes:

Greater Mark of Scaling Ability Power / Greater Seal of Scaling Ability Power / Greater Glyph of Scaling Ability Power / - You Guessed it this is AP Teemo, and AP Teemo is used with AP Scaling Per Level Runes.

Greater Quintessence of Ability Power - Since we have a slight edge against attackers, Why not counter the Magic Damage we will be taking.

Items:

Amplifying Tome / Health Potion - Allow for early AP and survivability for harassing.

Mejai's Soulstealer - AP per Kill is always Nice :) Not hard to fill one of these puppies if playing even decent.

Malady - Since we already have Amplifying Tome Malady becomes the next item on our item list.

Sorcerer's Shoes - Recommended for Magic Pen.

Rabadon's Deathcap - 30% Ap plus 120 = Perfect!!!!!

Hextech Gunblade - Spell Vamp from Dart and Mushrooms is better than lifesteal, Plus Damage and AP.

Guinsoo's Rageblade - for more damage, attackspeed, and AP.

Runes:
Greater Mark of Magic Penetration / Greater Glyph of Magic Resist / Greater Quintessence of Magic Resist - Magic Pen, is used to get the most out of the magic on hit effects also known as procs.

Greater Seal of Scaling Ability Power - AP Scaling Per Level.

Items:

Doran's Ring - Allow for early AP and survivability and Mana Regen.

Sorcerer's Shoes - Recommended for Magic Pen.

Rabadon's Deathcap - 30% Ap plus 120 = Perfect!!!!!

Lich Bane - Blinding Dart Attack Rape!!!!

Deathfire Grasp - After you Deathfire Grasp+ Lich Bane + Blinding Dart = Dead Tank.

Hextech Gunblade - Spell Vamp from Dart and Mushrooms is better than lifesteal, Plus Damage and AP.

Madred's Bloodrazor - If facing a high life team with decent damage out put, ex. Dr. Mundo Vladimir

This Video is a tutorial about how the three item combo works.

This Video shows some unique places and uses for your mushrooms.

This site has pictures for reference to place Shrooms