As a DM, what's the best non-combat encounter that you like to use? Some examples might be:

• A wood woad protecting an ancient fungi-infested tree requires a toll of 1sp in order for the party to pass.
• A harengon is tending to his orchard. He is willing to sell any of his fruit for 1cp, and eating the fruit grants 1d10 temporary HP.
• In the middle of the path stands an ancient wishing well. Whoever throws in a coin gets inspiration, and then the well disappears.

I personally love the first one, as it makes travel a bit more interesting. What are some of your favourites that you have come up with?

My personal favorite was a bard that was in the center of one of the smaller towns. I just had him there playing his instrument and singing as almost a side-point, but one of my players decided to go up and try to sing along. This ended up turning into an impromptu competition between them, and the bard wrote a recommendation for the monk in my party to visit the School of Harmony, a bard school in one of the central cities. This has now become one of the players biggest goals, and he practices his instrument in the down-time during long-rests.

I introduced a character I simply called the Tortle Tea-Trader, who was exactly that - a tortle who sells different types of teas. She was also in a weak spot between the material plane and the feywild, and is native to the latter. Her teas were essentially one-use items which you needed to use during a short or long rest, and they gave bonuses until the next long rest. The player (my Fiancee) left the weak spot and returned to find it was gone - the material plane had returned. I was threatened many times that "The Tea Trader had better show up again!", because she wanted to buy some tea!

She ended up getting some Bravery Tea and a couple of others I can't remember right now. The Bravery one is going to give advantage against effects which cause the Frightened condition.

For another non-ombat encounter, the entire party loved meeting a gnome herbalist and her incredibly fat bear who she feeds honey. The barbarian (who can speak to bears) asked if the bear was a slave, to which I replied in the most contented voice I could: "Noo... I'm happyyy :)". The whole party quites this regularly!

Bst non-combat encounter was with a homebrew creature called a Pressure weird. It sucks the air from around itself to create a vacuum, and is a large eel-like creature made of thunderclouds and lightning. It only wanted to play - and the characters realised. They spent a good few rounds of "combat" trying to work out how to get past it without hurting it, as every time someone moved, it would chase them like a cat chasing string! It also had the ability to pounce instead of making an opportunity attack, so it could chase people down who moved away!

I created a magic candy shop in one of my Underdark cities, owned by a woman Who Speaks In Exclamations! and owns a Blink dog high on sugar. My players had a blast trying to get her to slow down long enough to sell them sweets.

I also like using skill challenges. I've done them in dungeon chase scenes, for infiltration missions, and my homebrew death mechanic my players dubbed God Court. I like allowing the whole party to solve problems and tense social encounters creatively, when I can.

This was mildly combative but I really enjoy a low level encounter when the party gets sprayed by a giant skunk which causes minimal damage.  A NPC or demigod then condenses the spray into "funky skunk" pellets which can be thrown at enemies.  Little kids love the idea of being sprayed by a stinky skunk and it gives the party a nice low level, consumable magic item.  

I also like encounters with merchants selling potions with nebulous descriptions like, "This is the best thing a warrior could drink!"  It may be soured milk, wine, or a potion of heroism.  Whatever it is, once they actually use it, the NPC is long gone.  

Some fun parts of an adventure can be when the DM justs sets the players loose inside an inn. We did it in Rime of the Frostmaiden once and it was really fun. There were a bunch of NPCs we could interact and roleplay with and it helps us get more information on the world. When we did it, there was a crazy gnome conspiracy theorists who had a bunch of wacky ideas about the mystery we were trying to solve, there was a bunch of barbarians in the corner that you could gamble with, there was a bard that was really just Nacho Libre and we could get him to play songs for us and give us useless information, there was the bartender who could provide us with news and he could gives us equipment like axe beaks. There was also a bunch of dwarf women (bearded as they always should be)who hired us to recover a sleigh full of iron ingots they had lost to goblins. 

There was also the time we accidentally stole the entire hoard of an ancient white dragon (we were level five). We managed to talk our way out of being killed and actually gained a powerful ally over the goal of killing the same enemy. 

Another time, in the same campaign, an avalanche was approaching our party. Since I was a monk, I was able to out run it to safety, while the rest of the party was buried. They all had one turn to prepare and it turned out to be pretty cool. The barbarian and paladin anchored themselves to the ground, the cleric cast bless on his team, and the storm sorcerer ran straight towards the avalanche. He then cast thunderwave, in an attempt to slow down the snow, and since he was a storm sorcerer he flew ten feet into the air in an attempt to get over it. Because of all this, the party suffered from less harmful effects and were easier to dig out with the shovel I just so happened to be carrying with me. Challenges like that that require creative uses of your abilities and teamwork can be really fun.

Duffinsmertz the traveling Kobald merchant who brings to us inators aka magic items  general goods and  bits and bobs galore he is my favorite  my brother made him as a parody and he's a hoot I put him in my games I liked him so much .

I'm stealing Duffinsmertz. That's hilarious

Do you know the old riddle with getting a load of carrots, a goat and a wolf across a river? That can be turned into an encounter quite easily. You can just reflavour it as much as you want. Maybe it's not about a goat, wolf and carrots but two feuding families of really old people who will start fighting if they get the chance, maybe you're in a time constraint so you have to make decisions on the run, etc.