First, I think it's important to distinguish between an obstacle and a hazard. An obstacle is an impediment to progress; a hazard is just a trap by another name--a trap that wasn't set by anyone.
Quickleaf went to the heart of the matter: what is the purpose--the narrative purpose--of the obstacle? How does the obstacle serve your campaign's story? How does it contribute to the fun? Keeping in mind that in D&D, everything actually does happen for a reason. Nothing exists unless you deliberately create it, and make the players deal with it.
There's a truism that says "the worst trips make for the best stories." The movies Vacation, The Sure Thing, Smokey and the Bandit, Sorcerer--heck, even Wizard of Oz, The Lord of the Rings, and The Odyssey--are interesting because of the obstacles faced and overcome by the protagonists.
Point being: don't include an obstacle (whatever that obstacle may be) just so you can watch the players play a guessing game of which skill ability check to make, and then everyone watches someone roll a die and do simple arithmetic. That just wastes time.
Instead, do include an obstacle that:
1. Adds an unexpected complication to the existing journey
2. Changes the destination of the journey
3. Changes the perception/goal of the journey
An example of 1 would be something like a wounded NPC that must be cared for. An example of 2 is having to track down the party's horses. An example of 3 is when the party discovers that the enemy agents they've been racing to get to the McGuffin are their best allies in battling the eldritch horror they've unwittingly unleashed.
Break down the classic road trip movie Vacation for fun obstacles that don't just add to the story; they are the story:
1. The rad car they thought they were going to drive is, instead, a crappy car.
2. The get lost and lose their hubcaps.
3. They visit strange relatives and acquire a cantankerous NPC to escort home.
4. They crash, lose resources, and have to make moral compromises in order to figure out how to repair their car and continue their journey.
5. Their escort dies.
6. An ongoing conflict with an NPC is resolved.
7. They reach their destination to find it not what it was, but having gained a closer appreciation for their family. And they get a big reward anyway.
All three examples are well-represented above.
Anyway, here are specific obstacles you can use. Just use them deliberately. Each one should result in an event that your players will bring up years later, when recalling the campaign.
1. The party finds a wounded [friendly NPC/unfriendly NPC/animal] and has to bring it along. Dealing with the NPC on an ongoing basis is interesting.
2. The party encounters a hazard (poison gas, water, vermin horde, "death energy", unbeatable monster, whatever) that forces them to discard vital gear or resources. Making tough choices, and having to improvise in future encounters is interesting.
3. The party encounters a boon (treasure, NPC offering a bribe, magic item, portal, whatever) that lets them bypass or abandon their current mission. Making tough choices about whether to stick with the mission or take the easy way out is interesting.
4. The "abandoned" structure they're exploring is inhabited by unfriendly, but not combative, creatures. Figuring out how to evict, avoid, or fight the occupants is interesting.
5. They encounter a room filled with [glass vials with unstable contents/dormant mummies/hanging chimes/caged animals/whatever]. Deciding whether to save time by barging through, or figuring out how to bypass the room without causing a commotion, is interesting.
TL;DR: don't just say "Here's an obstacle. Make an ability check. Ok, you overcome the obstacle/oops, you take damage try again." Instead, use the obstacle to create a memorable moment.
