This list includes as many Green/Blue cards I could find that cheat mana. Cards that allow you to play extra lands are counted as "ramp" for this list. Cards that untap lands are counted as "ramp" on this list. Cards that cause Lands to tap for Additional mana are counted as "ramp" on this list.

Notable exclusions;
0. Lotus Cobra is a good card, but I dont think it qualifies as "ramp" here
1. Mana Rocks are mostly ignored : For those that want to find them, this is a good resource (https://managathering.com/manarocks.html)
2. Mana Chumps (CMC != 1) : When I did my search, I was mostly interested in 1cmc chumps because there are fewer ramp options for 1cmc, making them more relevant. Some mana chumps that aren't CMC=1 are included here, but those aren't nessecarilly the best 2cmc options... You can find much better options by searching on Scryfall (this search should cover them)
3. Ramp options (CMC > 3) : There are a lot of +4 cmc cards that can play 2 lands from deck, but they seem overcosted.
4. Mana Filter cards are ignored. Pay X to gain X (or less) mana of a different color is not ramp. (Pay X to gain X+1, however, DOES count as "ramp".)
5. Cards that tap both themselves and another permanent you control do not count as ramp. (Unbridled Growth, Saruli Caretaker...)

More Notes;
1. Green Sun Zenith with X=0 can search the Creature/Land/Forest card Dryad Arbor. (Note: If Dryad Arbor is in your hand, you must play it as a Land, and it has summoning sickness)
2. Some cards should be treated as different mana costs
  a. Beanstalk Giant = 3cmc (for its ramp part)
  b. Search for Tomorrow = 1cmc (for its suspend effect)
  c. Enter the Unknown is 1cmc, but you have to control a creature, so its unlikely to trigger on turn1 for 1mana.
  d. Crop Rotation is great since you can get ramp-lands untapped (mishra's workshop in a golos deck? bounceland trigger for shenanigans? yes please). Later in the game this card becomes a 0cmc landfall trigger/mana fixer.
  e. Elvish Reclaimer is similar to Crop Rotation, but with extra reliance on the fetched land providing some kind of advantage. Big lands like Gaea's Craddle and bouncelands are probably the way to go here.
3. Some cards on this list (Manabond, Caravan Vigil) are not that great, but are included anyway.


Below is an organized list of the cards that I'd actually consider running in a deck, sorted by CMC/Theme;

*0-mana (2)
  *artifacts
    *lotus petal
    *mana crypt
    *mox amber (control legendary creature)
    *mox diamond (discard land... effectively playing a land via artifact)

*1-mana (14)
  *land-deck
    *green sun's zenith (x=0; dryad arbor)
  *land-now
    *arboreal grazer (tapped)
    *krosan wayfarer
  *land-upgrade
    *wild growth
    *utopia sprawl (forest)
  *play-extra
    *exploration (+1)
    *burgeoning (+X, opponent's turn)
  *delay-land
    *search for tomorrow (or cmc=3)
  *creatures
    *joraga treespeaker (best t1 play probably)
    *arbor elf (untap land) (better than +1G, since combos with Land-Upgrades)
    *birds of paradise (1 mana, any)
    *sakura-tribe scout (play lands from hand)
  *artifacts
    *sol ring
    *mana vault

*2-mana (12)
  *land-play
    *three visits (forest, any)
    *nature's lore (forest, any)
    *rampant growth (basic)
    *farseek (not-forest, any)
    *into the north (snow-land, any)
    *sakura-tribe elder (basic, is-creature)
  *land-upgrade
    *fertile ground (+1 any)
    *wolfwillow haven (+1 green)
  *play-extra
    *explore (+1 play)
    *growth spiral (play land as resolution)
    *broken bond (destroys artifact/enchantment)
  *delay-land
    *khalni heart exhibition (2 basic, tapped)

*3mana (9)
  *like-cultivate
    *cultivate (is-cultivate)
    *kodama's reach (is-cultivate)
    *nissa's pilgrimage (is-cultivate, basic-forest, can upgrade)
    *beanstalk giant (basic, untapped, no-draw)
    *harvest season (X:your-tapped-creatures, basic, tapped, no-draw)
  *play-extra
    *azusa, lost but seeking (+2 play)
    *dryad of the ilysian grove (+1 play)
    *wayward swordtooth (+1 play)
    *journey of discovery (+2 play, or tutor-2 basic)

A better scryfall search;
( (o:"land") or (o:"add" and (o:"{G}" or o:"{U}" or o:"{R}" or o:"{B}" or o:"{W}" or o:"{C}" or o:"{M}") ) or (o:"add" and o:"mana") ) -t:land cmc<=1 id<=GU legal:commander
https://scryfall.com/search?as=grid&order=name&q=%28+++%28o%3A%22land%22%29+or+%28o%3A%22add%22+and+%28o%3A%22%7BG%7D%22+or+o%3A%22%7BU%7D%22+or+o%3A%22%7BR%7D%22+or+o%3A%22%7BB%7D%22+or+o%3A%22%7BW%7D%22+or+o%3A%22%7BC%7D%22+or+o%3A%22%7BM%7D%22%29+%29+or+%28o%3A%22add%22+and+o%3A%22mana%22%29++%29++-t%3Aland+cmc%3C%3D1+id%3C%3DGU+legal%3Acommander&unique=cards