General Intensity:
* Extremely
* Highly
* Exceedingly
* Remarkably
* Notably
* Significantly
* Deeply
* Intensely
* Thoroughly
* Absolutely
More Informal:
* Really
* Super
* So
* Quite
* Pretty
* Awfully
* Terribly
Emphasizing a Degree:
* Utterly
* Totally
* Completely
* Entirely
* Perfectly
* Radically
* Profoundly
* Immensely
* Enormously
For Specific Situations:
* For size or quantity: Huge, vast, massive, colossal, immense
* For speed: Rapid, swift, brisk, speedy
* For importance: Vital, crucial, essential, paramount, indispensable
* For beauty: Gorgeous, stunning, beautiful, magnificent, breathtaking
The best synonym for "very" depends on the specific sentence and the level of emphasis you want to achieve.