1) Birds of Paradise - what is not to love?
2) Llanowar Elves - see above with the ability to beat for one.
3) Rancor - soooo good!
4) Eternal Witness - just about the best green creature ever
5) Wellwisher - I love elf decks..and mass life gain
6) Defense of the Heart - Love this card!
7) Thrun, the Last Troll - Hexproof is the new shroud!
8) Chameleon Colossus - Remember playing him in elfball and him hitting for 200+ dmg!
9) Imperious Perfect - An elf lord, thats an uncommon, that makes elves? AWESOME!
10) Tarmogoyf - so so good!
11) Troll Ascetic - Like Thrun, except better!
12) Sakura Tribe-Elder - land is good..especially when it comes with a free guy
13) Fastbond - dumping land into play is fun..and makes your opponent angry
14) Tooth and Nail - because doing two awesome things is great
15) Berserk - Its so good and can win games otherwise lost.
16) Regal Force - like I said.. I liked elfball a lot
17) Harmonize - what? green gets card draw?
18) Garruk Wildspeaker - The original green planeswalker
19) Priest of Titania - mana a plenty
20) Doubling Season - I love cards that double things
1. Llanowar Elves This guy is all green: he is an elf, he gives mana ramp and he lives in Llanowar. He has been around from the beggining of MTG.
2. Wild Mongrel More than a tournament successful deck was built around this puppy.
3. Regrowth It has raw power, but what I like the most is its green flavor: it makes things to regrowth. And the art is beautiful.
4. Yavimaya Ants I love these insects, they have won me more than a game. Yeah, there are "better" creatures in green, but this is my list and I accept no comments nor complaints.
5. Fastbond So broken and funny. And nothing can't beat that illustration.
6. Crumble You can destroy your opponent's artifacts, but I won one game Crumbling my own tapped Nevinyrral's Disk, gaining 4 life and surviving to swing for the win in my turn.
7. Blastoderm My mexican friends used to called him Blastoenferm. You can translate that as Blastosick.
8. Elvish Hunter An annoying elf that gives you great tempo advantage.
9. Elves of Deep Shadow Very flavorful, specially with The Dark art.
10. Wood Elemental Some day, I will make a deck around this guy, and it will be a killer deck.
1.)Kamahl, Fist of Krosa
6.)Omnath Locus of Mana
7.)Patron of Orochi
10.)Defense of the Heart
11.)Myojin of Life's Web
13.)Tooth and Nail
19.)Green Sun's Zenith
20.)Sakura Tribe Elder
Off the top of my head, here is my list of mono-green cards. I am sure I have missed some, but these are what came to mind.
1. Fastbond - The most broken green card in the game.
2. Oath of Druids - Format-defining in Vintage to this day and completely suppresses aggro in any format where it's legal.
3. Survival of the Fittest - EDH and Cube staple, powerhouse in Standard and Extended, broken Legacy in half.
4. Channel - You may need to build your Constructed or Cube deck around this card (before it was banned or restricted in almost every conceivable format), but no other card can reasonably threaten to end the game immediately on turn 2.
5. Green Sun's Zenith - Enables so many decks in Legacy and powerful enough to have been banned in Modern.
6. Noble Hierarch - Best mana creature in the game, with a useful ability to boot. This is terrific in every format where it's available.
7. Scavenging Ooze - Amazing body and utility which provides graveyard hate and lifegain in the maindeck.
8. Tarmogoyf - Arguably better than Ooze in the Constructed formats due to the existence of tempo decks, but nowhere near as good in EDH and Cube
9. Birds of Paradise - One of the most powerful starts in Magic since 1993
10. Natural Order - Cheating big fatties into play since Verdant Force, it's usually lethal in Legacy
11. Llanowar/Fyndhorn Elves - These have been outclassed as mana ramp spells, but their creature type is still very much relevant in Legacy as well as in EDH and Cube. Honorable mention to their newer cousin, Priest of Titania, who is much more powerful in more casual formats.
12. Craterhoof Behemoth - This almost certainly spells "good game" when it hits the battlefield
13. Primeval Titan - Dominated Standard, sees reasonable play in several Legacy decks, and a hugely popular casual card that found its way to the EDH ban list.
14. Wall of Blossoms/Wall of Roots - These are not functionally identical by any means, but they're often found in the same decks. These were the primier green creatures in Standard (seeing play in Rec-Sur as well as Stupid Green) and continue to be staples in EDH and Cube.
15. Rancor - One of the first "Enchant Creatures" you could cast in constructed without feeling embarrassed.
16. Eternal Witness - A terrific ability on a solid body, enabling many tricks in Legacy, Cube, EDH, and Modern alike.
17. Glimpse of Nature - You have to build your deck around this card, but it sees or saw play in Standard, Extended, Legacy, and even Vintage, in addition to being a casual favorite.
18. Regrowth - I think this is a bit overrated in a vacuum, but in a format like Vintage, re-buying your bombs or even setting up a busted Gifts Ungiven pile is backbreaking.
19. Tooth and Nail - A defining card in Standard decks of its time and a card Timmies embrace in slower formats.
20. Birthing Pod - The currently oppressive force in Modern also sees some play in Legacy. An incredibly fun card that I almost never pass if I have an opportunity to build a Cube draft around it early.
* Sylvan Primordial - As far as I know, this saw no serious Constructed play, but its effect is ridiculously broken in a multiplayer environment.
* Joraga Treespeaker - The best ramp creature you can draw in Cube.
* Rofellos, Llanowar Emissary - A Standard and casual powerhouse which has surprisingly seen limited play
* Overrun - Perhaps the biggest limited bomb on the list with some Standard play, although it hasn't seen as much play in older formats
* Quirion Ranger - An innocuous card that actually provides surprisingly useful ramp and utility; a staple in decks as diverse as Stompy aggro and Combo Elves!
* Sylvan Library - I'm not a huge fan of this card, but other players have used this as the green Necro in Legacy, EDH, and Cube.