I have run quite few encounters for 4e. My group has played Keep on the Shadowfell and then we started back on 1st level and have just reached 8th.
I've seen a number of encounters with different criteria and styles.
First, I would say that anybody who has access to D&D insider should definately check out Dungeon Magazine and if you don't have access to it, you should get it. While I have not used any adventures per se, I have found a LOT of encounters adaptable to my own campaign and many of the encounters give me new ways of building them. It is a fountain of ideas.
Having said that, I have found that encounters that have a goal besides a straight up fight to be the most exciting. Rescuing a prisoner before he dies, recovering a magic item before the bad guy flees with it, escaping a trap before it goes off are all examples of this. Here are some encounters I have run or been a part of:
This one is from dungeon. It is essentially a dungeon like room that has several platforms at different levels. Enemies are spread out on the the platforms encouraging the PCs to work their way up the room. In addition to that the room is filling with a dangerous substance (could be lava, water, whatever you like) and after a few rounds the lower platform is engulfed, then 2 more rounds later, the next platform is engulfed and so on. This encourages movement not only by the players but also by the monsters. This is a great example of a dynamic fight.
Another fight I ran just last session was made up of mostly controllers. It was essentially a cultists lair but it had the main area of the chamber, it had some stairs with a ledge that was 10' high and I had four large bird cages haning about 15' up he wall in each corner of the room. At the beginning of the fight, all the PC's except one were in the centre of the room, a twilight encanter and a medusa were on the ledge and I had Harpies in the cages. One PC had snuck into the room as a rat and had climbed up to the ceiling rafters. Originally, the PCs thought that the harpies were captives but as the fight progressed they realized that the cages acted as cover for the harpies providing protection and the harpies could get out by opening the cage door because it was not locked. With the harpies able to pull the PCs, the twilight encanter able to bind or blind the PC and the Medusa able to slow, immobilize and turn them to stone the PCs were always on their toes and could easily be caught by themselves. I sprinkled in a few dopplegangers to do some damage and it was a lot of fun all around. The 10' ledge forceed Pcs to go up there to tackle the monsters since they were out of melee reach. This isn't a great example of terrain use but does serve as an example how mundane rooms can be a bit more interesting with the proper creature types.
Another fight I was a part of as a player was in a burning corn field. Fire and smoke created concealment and the rows of corn made it so anybody could pop out from nowhere. It was a hide and seek type fight that worked really well.
Yet another fight was at a gnoll encampment that had lots of tents and cages of prisoners. We showed up, kicked some @ss and then the DM had a returning war party come from the otherside of the clearing. We were caught in the middle and then had to make the best use of the tents and crates in the area to get some cover.
While none of these examples provided contain any sort of fantastic terrain each encounter featured an element that made the terrain a tactically superior option in combat. I've found there to be two key things. First, find a reason for the PCs use the terrain or be forced to make use of it, otherwise the terrain just sits there. Secondly, fights where the PCs are mixed up with the bad guys (this could be surrounded, caught between two groups or interspersed with them) makes things more dynamic.
As a DM, if you don't give the PC's a reason to use the terrain and make options that make the use of terrain an optimal tactic, then PCs will just stand there and slug it out because THAT option becomes the superior tactic.
I have found this to be the most radical change in thinking from 3e to 4e. I sometimes forget to do this and it quickly turns into a boring fight.