General Size:
* Huge: Very large
* Massive: Extremely large
* Enormous: Immense in size
* Gigantic: Extremely large
* Colossal: Very large and impressive
* Immense: Very large and impressive
* Whopping: Extremely large
* Ginormous: Very large and impressive (a blend of "giant" and "enormous")
Quantity:
* Tons: A large amount of something
* Loads: A large amount of something
* Loads: A large amount of something
* A ton of: A large amount of something
* Plenty: More than enough
* A lot: A large amount of something
* A bunch: A large number or quantity
Informal/Humorous:
* Mega: Very large or great
* Humongous: Extremely large
* Jumbo: Very large
* Biggie: Large or important
* Massive: Very large and impressive
* Epic: Extremely large or impressive
For People:
* Beefy: Muscular and large
* Chunky: Heavyset
* Hefty: Heavy or large
* Big boned: Having a large frame
Other:
* Major: Important or significant
* Major league: Extremely large or impressive
The best slang word to use depends on the specific context. For example, "huge" is a good general term for something very large, while "mega" might be better for something impressive or cool.
Remember, the meaning of slang can vary depending on the region and the group of people using it.