So we all know about the brand new party coming together to fight goblins, kobolds, and bandits attacking a small town. But what I wanna know is what OTHER good "intro" monsters are there? 

I wanna know what you guys have used as "the-first-fight (tm)" in terms of monsters, AND context?

Ogre Orcs Zombies etc. Depends on the level of the party, Generally if its a long term campaign start at level 3 or if you really have newbies one.

We pretty much always go from 1->somewhere in Tier4 (20 once!). My party likes the "started from zeroes, now heroes" trope lol

So they'd all be level 1

Mimics are great for this. You can build a real sort of "haunted house" atmosphere for the players as they find themselves in a situation where anything around them could be a mimic in disguise. You could have a lot of fun with the various low-level ambush monsters... toss in a gelatinous cube once the players get so used to looking out for objects they don't find anything suspicious about a perfectly clean 10x10 hallway until they walk right into the transparent cube in the middle of it. Maybe slap a gray ooze or two on a brick a wall and see what happens.

Blights are another starter standard.

Entirely dependent on the session zero when I'm the one running the game. When my regular DM starts us off, yeah it's typically Goblins, Orcs, Kobolds, Xvarts, and numerous monsters or beasts typical in their landscape setting. Not terrible, but it becomes predictable and afterwards encounters like that get blown through because we develop strategies in order to beat them while maintaining our resources.

When its my game I attempt to diversify not only for the landscape, but also varying degrees of difficulty/deadliness within the CR range. There are quite a few monsters which are more potent than others which get overlooked because they have low damage, but bring different abilities to the table which proves difficult for beginning level adventurers to deal with. Giant Poisonous Snake, Cockatrice, Shadow, Skulk, Gas Spore, and Quicklings are some that come to mind specifically because of their inherent abilities along with some of the damage they deal, which in turn makes them more difficult for beginner encounters. Those are all CR 1 or lower too! Believe it or not, I've nearly TPK a party of four level 3 adventurers with a grouping of them appropriate to the setting (the quickling swarm caused the most issues next to the giant snake).

Giant beasts and nothics

A cemetery with skeletons, zombies, and something “big” that’s their master. Either another undead such as a shadow or a ghoul or make the cemetery’s care keeper a cultist. 

I started my most recent party off on a ship, heading on a grand quest to recover a stolen artefact alongside 300 of their nation's best warriors.

As level 1 characters, at night the 4 PCs were put on watch duty together as the ship lay at anchor off-shore. During the night a strange visitor (actually the BBEG) Dimension Door'd onto the ship and enacted a spell before leaving again. The hatches downwards were all magically sealed preventing the other warriors getting out. Suddenly huge bio-mechanical tentacles burst out around the ship, latching on... yes it was a Mecha Kraken ^_^  But I didn't have them fight a kraken at level 1, obvs, instead they were able to attack the individual tentacles. The tentacles paid them no heed as the kraken was intent on taking down the ship not a few measly humanoids.

But the tentacles also spewed out muddy sediment goop, made of stuff from the bottom of the sea that formed into humanoids. These were sub-goblin level stats (commoners if I recall right, except they hit for 1d6 damage and could fling mud for 1d6 damage as well) and moved only 20 feet a turn. The mud-men went for the PCs, who began to realise that the ship was doomed. Magic kept all other occupants trapped below, doomed as the kraken began to break the ship apart. The PCs made it into a lifeboat...

They rowed away and after the ship went down were chased by the mecha-kraken. It couldn't get close enough to use its real attacks, but it managed to fling more little mud men at them at range, and spat very weak acid. Eventually the PCs made it to the shallows where the kraken couldn't follow. Two of them were on death saving throws, one of whom had failed 2.

That was the first encounter of my campaign. All of the PCs survived and are now level 9.

So, the point of all this: don't worry about the type of creatures. Think of a scenario or theme, then reskin whatever you have to. Even reskinned commoners are a terrifying threat when your ship is being torn apart by a kraken.

Don't forget undead! Necromancer raising a band of skeletons to terrorize a town is some classic stuff, and sets up a future bad guy in the necromancer.

I've always found the best encounters always have layers. Even at Level 1, an encounter/quest with layers and more-behind-the-screen is what brings the world to life. That said, I think a great way to start off a campaign is with a hag.

Hags are great because they are devious, cunning, and manipulative, while also physically/magically strong. Also, hags like to change form and meld into society where they can sow their destruction and evil plots - making it a great enemy for the PC's to actually face in a roleplaying situation.

Now, of course, the PC's cant fight the hag at level 1, but they can fight all of her proxies that she uses to make deals or steal children. Perhaps she has a group of Darklings or even Quicklings (evil fey) that she uses to steal, pilfer, or carry messages. Trying to capture and kill these little buggers could be very fun and provide clues as to the hags nature. Then, when they reach 3rd level, they can take on the hag herself, having rooted out an enemy of the townsfolk over the course of a couple of levels and from there can branch out into the wider world. 

Evil fey will surely have them talking about the session more than the classic kobold camp in the nearby cave. 

Good luck!

Fiends are normally considered a high-level thing, but they scale all the way down to CR0. Can be a good way to start out if fiends are the primary antagonists. Alternately, they may be summons of a cult that the party needs to take down.

Zombies, skeletons 

How many players? You need to scale the combat encounters. For two level 1 characters two 1/8 CR monsters, or one 1/4 CR monster is easy to normal difficulty encounter. I recommend to learn the challenge rating table. It makes much easier to scale difficulty of encounters. Good thing about Kobolds and Goblins is that they fit for any environment and they are bloodthirsty monsters. Bandits are bit more complicated on alignment scale because they are humans. Sometimes players want to side with bandits.

The beginning of my homebrew campaign used sahuagin capturing survivors of a capsized ship and making them fight each other to the death for fun. (Either this *is* the beginning to the Tomb of Annihilation module, or I was heavily influenced by it). My players loved it - they formed their adventuring group, and wound up working together with the other main group to fight the sahuagin instead of each other. 

That other group even went on to be their friendly rivals in the adventuring business.

Sort of like what VanZoeren said:

Start your players off fighting in a gladiatorial arena. Makes for a fun opening and provides a common link among all characters.

In this 1st-level adventure of mine I used an imp as main villain of the first small dungeon, together with zombies and skeletons:

https://www.dmsguild.com/product/496145/EBERRON24-The-haunted-shrine