Firstly you need to know how to add a spell to your character. This is done by typing .char learn <id>
Fill in the <id> section with one of the following id's, remove the <>
GM Spells
265 - Area Death - Simply kills everything around you that is a "enemy".
11 - Frostbolt of ages - Does 1k damage to anybody or anything that is targetable.
2583 - Debug Spell Reflection - Reflects all spells and attacks.
31984 - Finger of death - "Strikes an enemy with the finger of death, inflicting 20000 shadow damage upon them, their children, and their children's children."
Useful Spells
48018 - Demonic circle - Places a point you may teleport back to for 6 mins.
48020 - Demonic Circle: Teleport - Teleports you to your circle.
Fun Spells
73914 - Necrotic plague (Highest Damage) - Deals 150k damage after five seconds.
70337 - Necrotic plague (Normal Damage) - Deals 50k damage after five seconds.
68981 - Remorseless Winter (Normal Damage) - Deals 7k to 7.9k damage every second to all those around you. 45 Yard Range.
74275 - Remorseless Winter (Highest Damage) - Deals 14k to 15k damage every second to all those around you. 45 Yard Range.
70053 - Revive Champion - Summons a Argent Champion to fight for you.
32819 - - Worgen Form - Turns you into a worgen.
30167 - Red Ogre Costume - Turns you into a red ogre.
14888 - Arei Transform - Turns you into a ancient.
70900 - Dark Transformation - Turns the target into a undead behemoth. (Increases size and damage dealt.)
5154 - Reindeer Transformation - Turns your mount into a reindeer.
55098 - Transformation - Turns you into a mammoth increasing stats and granting immunity to stuns etc.
65108 - Black hole Explosion - Deals 21k damage to enemies around you.
65333 - Explosion - Deals 47k to 52k damage to all enemies around you and puts out fires!
15474 - Web Explosion - Stuns all enemies around you for 10 seconds.
71469 - Aether Burst - Inflicts 15k damage to target as holy damage. Unlimited range.
38987 - Focused Bursts - Inflicts a random debuff on the target.
Fun Items
192 - Martin Thunder - A gm weapon that uses the area death spell as it's use.
23864 - Torment of the Worgen - Turns you into a Worgen allowing you to deal extra shadow damage.
EDIT: Added more.