Rammus, The Armordillo is a tank champion that focus on destroying and annoying his enemy's with his speed and his taunt.

Pros:

Very Fast
Good Ganks
The most tankiest champ
Good mid-late game
3 seconds taunt
Good after many nerf's

Cons:

Weak early game
You can easily counter jungle him
He doesn't speak
Not a good clearer in the jungle

Jungling:For runes you need as much armor as possible because of rammus's passive. You need attack speed too because you can clear easily the jungle.
Support: For support you need classic support runes (mark's and seal's with armor, glyph's with magic resist and quint's with gold/10 seconds)

Rammus is a strong jungler, with exceptional ganks. Powerball allows him to initiate ganks suddenly, and Puncturing Taunt is a strong CC ability with a fairly long duration.
Note that Rammus's Powerball, whilst it still does damage, it has no crowd control effect on Baron Nashor or the Dragon. Also note that Puncturing Taunt now has absolutely no effect on Baron or Dragon (it will not reduce armor or force either to attack you). Both skills will still affect all other neutral creeps as normal.
Starting items: Hunter's Machete, Health Potion x5
Skill progression: Defensive Ball Curl → Powerball → Defensive Ball Curl → optional from here on.
Jungling route: Blue Golem->Red Golem (smite)->gank (if you want)->Wolfs-> Wraths-> Golems

Powerball can interrupt jump moves such as Jax's Leap Strike or Tristana's Rocket Jump mid-jump.
Abilities such as Jax's Leap Strike, Garen's Decisive Strike and Xin Zhao's Audacious Charge will not stop Powerball if Rammus is accelerating in the opposite direction.
If an enemy Renekton uses Slice and Dice through Rammus while he is using Powerball, the ability won't be canceled.
Defensive Ball Curl increases Rammus's armor, which increases his damage due to Spiked Shell by (10/15/20/25/30).
Powerball can be used as an effective escape mechanism. It also has a slight knock-back effect, and this allows for you to run into pursuers to momentarily disable them.
As Powerball speeds up continuously after the initial cast, it's sometimes better to let it speed up in a brush before rolling at someone.
Flash can be used while in Powerball to jump across a minion wave to catch your opponent off-guard.
Powerball can hit stealthed champions such as Twitch, Shaco, Akali, or Evelynn, dealing damage and knocking them back. It will also work against a Camouflaged Teemo, knocking him out of stealth. This can be useful for chasing them if they go stealthed at low health.
You can use Powerball then use Teleport to be at a high speed when reaching your destination.
Powerball will damage and slow enemies reviving from pseudo death ( Guardian Angel or Zilean's Chrono Shift) or Zhonya's Hourglass, granting an easy kill.
Puncturing Taunt can be used on enemies pushing your turret to make them attack you and causing the turret to attack them. It can also be used to take the focus off more squishy allies, allowing them to deal more damage than they would have had they been the focused target.
Puncturing Taunt can also be used to "pull" enemies towards your team as an enemy will be forced to get into attack range to hit you. This is more effective with melee champions whose attack range is shorter than ranged ones.
When using Tremors, you can use all your spells to keep enemies in range of this spell in order to maximize damage. This is possible because the ultimate is not channeled.
Tremors affects turrets, making Rammus a very good pusher, especially lategame when he can tank the turret for his team.
Backdooring is a simple matter because you can easily use Powerball to run away before enemies catch up.
Rammus can use Tremors while using Powerball, making it very useful for destroying towers or champions that are low on health and escaping.

Thank you for watching my guide and i hope it will be helpful. Rammus is my main champion.