Commander as a format is all about the efficiency of your removal. Unlike a one-on-one format like Modern, you've gotta get the most out of each card your play.
Thoughtseize, for instance, is an extremely powerful card in just about every 60-card format, but completely unplayable in EDH. This is because in Commander, spending a card to remove a card is a net negative for you. To go truly even, you need to spend a card to remove three cards, since that's how many opponents you're up against.
Thus, the board wipe, aka sweeper, remains a necessity in even the most casual of decks. Usually the downside of casting a card like Wrath of God or Farewell is that you have to take your turn off to reset the battlefield, theoretically putting you last in the order to begin rebuilding your boardstate. That's why the best sweepers are the most efficient, they either cost less mana, give you some benefit, or deal with multiple types of card.
Now, we all know about the cards Blasphemous Act, Damn, and my personal favorite: Vanquish the Horde, but I'm here to tell you about some of the less-popular wipes and why you should consider including them.
Doomskar
Probably the most popular of the sweepers here, Doomskar is still an often-overlooked piece from 2021's Kaldheim. Though foretell is a rarely-revived mechanic, meaning you're not likely to be bluffing very hard with the face-down part of it, paying two mana to let it sit in a zone that's practically uninteractable is nice. The fact it turns into a three-mana creature sweeper later on grants you the chance to follow it up with some other spells on that turn.
Hour of Revelation
In the same vein as Vanquish the Horde, Hour of Revelation gets cheaper when you want it, and is only really six mana before the board has hit critical mass. Instant-include in mono-white decks, but a little harder to justify the more colors you add due to the irreducible triple white in its cost.
Sunfall
A five mana exile-all-creatures spell is not terribly overcosted, and it has the upside of making a big-ol' token that becomes a creature for two mana whenever you want. A favorite of control players in Standard, I would expect the cash price on this card to come down when it rotates out of the format.
Out of Time
Enchantment removal isn't quite as common as it probably should be in Commander, which means that the likelihood of this getting dealt with is pretty low. Even if it does get removed, you're forcing an opponent to spend resources taking it out for what only cost you three mana.
Small bonus: This card doesn't allow commanders to go back to the command zone when they're phased out, meaning you don't have to worry about someone recasting it on their turn.
Last One Standing
The "wider" the board is, the better Last One Standing is. Chances are, if there's 20 1/1 Goblins on the board, and 10 other big scary creatures, you'll only be leaving a puny gobbo on the battlefield. Since you're already running at least black and red, you probably have efficient single-target removal to handle that last creature if it does happen to be worth taking out.
Terisiare's Devastation
I'm not gonna act like this one should see more general-use play, but looking at EDHRec makes me think this card is just not being used outside of the precon it was included in. Any black+ artifact deck should at least be considering this card. Gets around indestructible, ramps you with artifact tokens, and you can choose whether to clear the board or keep the heavy-hitters around.
Oversimplify
Oversimplify might be five whole mana with a drawback, but it does exile, and it's in two colors that don't have many options for sweepers anyways. If your local Simic player ever complains about not being able to deal with a big boardstate, show them this card.
Depopulate/Shatter the Sky/No Witnesses
These are all the same card: Day of Judgement with a semi-symmetrical card draw effect. If you're going for a truly budget deck these are good options that aren't overcosted.
Terror Tide
Terror Tide is, frankly, a hilarious card in graveyard decks. It beats indestructible due to giving -X/-X instead of destroying, and your wallet will thank you for running it over Damnation.
Planar Collapse
I know what you're thinking, "who wants to wait a turn to wipe the board?" That's fair in some situations, but you gotta consider just how efficient a two-mana board wipe is. Waiting a turn sucks, sure, but there have to be more than 2,000 decks that want this. Nobody's gonna play a creature until this thing resolves anyways, and it means you get first dibs on casting creatures after it fires.
P.S. You could probably find a fun janky way to abuse it such as putting Shielded by Faith on a Sun Titan.
Anzrag's Rampage
One-sided artifact sweeper that cheats out a creature for a turn is pretty great for five mana. It's too new to actually call it underrated, but I recommend it all the same.
Fade From History
This card should be in every single mono-green and gruul deck that doesn't consist of over 50% enchantments. Four mana to clear the mana rocks, the artifact creatures, and value pieces like Rhystic Study or Smothering Tithe is great.
Everything Comes to Dust
This card is a slam-dunk include in any white+ deck that wants to go wide, especially if it's focused around a particular creature type. Magic has so many creature types that you rarely have to worry about this not hitting your opponent's biggest threats, and in the very worst case scenario, it's gonna be a convokable sweeper that exiles artifacts and enchantments.
One More Thing...
This list isn't gospel, you shouldn't run all of these cards in all of your decks, but you should be looking at them to take up those slots in the 99 that aren't just Wrath of God, Damnation, or any other yawn-inducing card that is generically good, but might not actually be the right fit for you.