Mana producing is the most important part of magic. Being able to play all your spells is vital. Some land cards obviously have more value than others. Some have less value than others: see Wintermoon Mesa. Whether or not you count these cards towards your mana ratio depends on if the card can generate mana and what type of deck you have. These are my favorite 20 lands.
20. Dryad Arbor
A free Llanowar Elf is nothing to sneeze at. Though that's all he does and doesn't actually count as an elf which is why he is good, but not great.
19. Mishra's Factory
One of the better lands to play in either artifact/metalcraft decks or with multiples. A 2/2 attacker by turn 2 is nothing to sneeze at and the fact that it probably won't be killed by sorceries is a nice bonus. Late game doesn't do much which is why multiples help.
18. Kessig Wolf Run
Probably won't dominate any games but it does give any creature you have the ability to pump. Late game this thing will cause problems. Early game might not do much.
Give any creature you control the ability to pit fight another. Oh and repeat as many times as there are creatures your opponent has. Just get a large enough creature and watch as he takes down your opponent's weenies one by one. Why I don't like it more - it doesn't produce mana and it costs 4 cards a turn isn't a tiny investment. OH, it's also a book.
16. Lotus Vale/Scorched Ruins
These can fix many mana issues you have, though it totally depends on how much you need different colors of mana verse speed. Scorched Ruins seems stronger to me as it gives you a 2 mana jump lead but you need a way to use all that colorless mana - thanks no mana burn!
15. Crumbling Necropolis
Really strong lands for decks playing all 3 colors. That being said, the more(comes into play tapped) you play, the more problems you are going to have in the beginning of the game. Perfect for control decks though.
14. Slayer's Stronghold
Giving any creature you play the potential to get haste is going to change how your opponent behaves which gives you an advantage. Oh and this card gives +2/0 and vigilance on top of it, so it can also block first turn?! Biggest downside is that all the haste creatures just happen to be red anyway.
13. Yavimaya Hollow
Regenerating happens to be underrated. The possibility of regenerating any of your creatures makes so many types of removal not nearly as effective or gives you card advantage.
12. Pillar of the Paruns
This obviously has to fit into the right deck. You need to be able to use the darn thing. But it's not legendary, so if you are running all multicolored cards - run 4 of these puppies.
11. Maze of Ith
It's best use is opponent deterrent in multi-player games. It does untap the creature and leave it for blocking. Can also save your own creatures due to combat tricks.
10. Vault of the Archangel
Deathtouch/Lifelink is one of my favorite combos. So giving all your creatures these abilities is just great. 5 mana a turn(essentially) isn't tiny but with enough creatures this becomes quite a threat.
9. Gavony Township
Very similar to number 10 except this effect is permanent. The newer sets abuse +1/+1 counters as well.
8. Ancient Tomb
Free Sol Ring. But slightly more balanced as 2 damage seems like a painful drawback, but still can create some huge advantage for you early game.
7. Strip Mine
So many combos can be derived from this card. But destroying your opponents best land for 0 mana is always great value.
6. Savannah/Underground Sea/Plateau/Tiaga/Badlands..etc
Dual lands are the best mana producing lands. No question. The five I placed ahead of this have the ability to take over a game with their other abilities while these are just simply mana producing lands. Lots of people like the tutor lands, but these are infinitely better.
5. Kjeldoran Outpost
Slow to get going, but eventually for essentially three mana creates a 1/1 every turn. You have to be able to use this effectively so it's not for all decks. But white weenies everywhere unite.
4. Thawing Glaciers
Also takes some time to get going, but given the course of a game this thing will help your draw chances late game so much.
3. Volrath's Stronghold
It's almost like cheating if you have a good creature or two that your opponent just doesn't have the right removal for.
2. Mishra's Workshop
Clearly only good in artifact decks, but that doesn't stop it from being my number 2. Basically a reusable black lotus in those decks. Play three of these in a row and welcome your own Colossus of Sardia.
1. Library of Alexandria
Turn one: draw a card
Turn two: draw a card
Turn three: draw a card
Turn four: draw a card
Turn five: draw a card
Repeat and opponent can't keep up.