Nature:
* Grass
* Leaves
* Moss
* Tree (some types, like pine or fir)
* Fern
* Frog
* Lime
* Pea
* Cucumber
* Spinach
* Lettuce
Other:
* Emerald
* Jade
* Money (often associated with green)
* Apple (some varieties)
* Traffic light
* Shamrock
* Slime
* Slime mold
Let me know if you want more examples, or are looking for nouns that are green in a different way!