TL;DR: "Fast mana" (i.e. Moxes and Crypt),
Sol Ring,
Birds of Paradise, and
Wild Growth are all "good."
Arcane Signet is generally an auto-include, and cards like
Land Tax and
Tithe can be incredibly useful. Beyond that, it's all mostly situational.
To the points already made, it's kind of a prisoner's dilemma: if you don't run ramp but everyone else does, you might fall behind in development. If you run it but nobody else does, you might find yourself behind in card advantage. If nobody runs it, the game might take longer. If everyone runs it, then the only thing that matters is who ramps hardest and/or most efficiently.
The answer really is "it depends," not only on deck construction (if you're a
landfall deck or have a 6 CMC commander, then it's definitely good to have) but also on what constitutes ramp and how you define good. If you're talking mana rocks, then generally I only
consider ones of CMC two or less to be "good;" rocks that are 3 CMC or greater are quite situational (3-for-1 is not very efficient,
Thran Dynamo is OK for slow decks at 4-for-3, and almost nobody runs
Gilded Lotus anymore at 5-for-3). Even in 3+ color decks, I will typically only run
Coalition Relic or
Relic of Legends because of the upside. The Talismans and Signets are more efficient. Fast mana, like the Moxes and
Mana Crypt are objectively good and almost required if you want to play competitively.
Sol Ring is as well because it is net one mana by itself, basically a poor man's Crypt. I'm of the belief that you never have to justify its inclusion, but rather need to find a very good reason
not to run it. I feel like almost every deck should probably also run
Arcane Signet.
Mana dorks are typically only a green thing, but do exist in other colors. The problem with them is that, as creatures, they are far more susceptible to removal than any other form of ramp. If they don't pay for themselves quickly, you'll end up going net negative.
Birds of Paradise is the premier mana dork. 1-for-1, and it taps for any color. If you can run Birds in the deck, you should. Then there are all the
elves that tap for one. Still at 1-for-1, they are very efficient ramp, but don't do a whole lot else unless you're playing elf ball or Raggadragga or something like that. Worst case, you can use them as chump blockers. There are more beyond that, but the more costly they are to play, the more situational they become.
Ritual effects, which serve as a one-off ramp, are very situational. In competitive where speed matters, they tend to be more prevalent and important to get you to the one important thing you need to cast. The slower or more casual the deck becomes, the less useful they become. Exceptions are things like
Mana Geyser, which tends to be more of a spell that ends games than one that is used for ramp. Good for competitive or if they enable a big turn, but not super helpful otherwise.
Mana doublers can be considered ramp too. Prominent in black with things like
Crypt Ghast, they're great in mono-black and maybe two-color decks with black, but outside of that you basically have to have an
Urborg, Tomb of Yawgmoth out for them to be of any value. There are things like
Zendikar Resurgent,
Nyxbloom Ancient, and
Caged Sun. The problem with them is that their casting cost is typically so high that they are just "win more" cards; if you already have seven mana to cast a Nyxbloom, you probably don't need to be tripling your mana and could be doing other things to further your board state. There are also effects like
Extraplanar Lens and
Gauntlet of Power, but they're kind of niche; both end up potentially benefiting your opponents. That being said, I have a
Maga, Traitor to Mortals deck that runs every single mana doubler and functional copy of
Cabal Coffers it can because the point of the deck is to make as much mana as possible and then cast X kill spells. I even run
Doubling Cube.
Then there's white ramp, which we just don't talk about. All it does is make sure you are on parity with other players in terms of land count. You won't get ahead with it, but you won't fall behind either. Notable exception is
Smothering Tithe. Salty card or not, if you're playing white and can run it, you probably should. Unless it gets removed immediately, it very quickly spirals out of control and puts you so far ahead, even if only for one turn. I guess it's kind of like a riskier ritual in that sense.
Green has a number of Auras that enchant lands to ramp. I wouldn't necessarily
consider them "good" because they typically aren't the most mana efficient and don't thin your deck as much as a
Cultivate, but they can pay for themselves faster if you're able to use them the same turn you cast them, and they can help with color-fixing.
Wild Growth is probably the best one of these. Another 1-for-1, and if you have a land and at least one other green mana, it pays for itself the turn it comes down.
If you're referring to traditional
Rampant Growth type spells or extra land drop effects like
Exploration in green, then yes, it is too good. Top of the Storm-scale, Wizards plz ban. The playgroup that got me into Magic (one person in particular) likes green a little too much... between a
landfall deck and an Azusa deck replete with
Eldrazi titans, it goes without saying that I'm biased against it. I still run it though usually; in two- or three-color decks with green, I almost always run at least
Rampant Growth,
Three Wishes,
Nature's Lore, and
Sakura-Tribe Elder, throwing in
Cultivate and
Kodama's Reach depending on the curve. The best thing about the latter two are that they
also put a land to hand, so you can at least guarantee that you won't miss a land drop for one turn.
I almost never run spells that
only put lands into hand. That's not ramp, just deck thinning and making sure you don't miss drops. It's paying mana without getting any back in return unless you can play the additional lands. The only exceptions I can think of are
Tithe and
Land Tax; if you don't go first, they let you keep a one-land hand because you're guaranteed to not miss your drops for at least the next two or three turns (respectively).
Gift of Estates is also OK, but it's two mana and you can only cast at Sorcery speed.