Ya, this would be nice as I've noticed that my PCs tend to walk over any encounters that are of level unless I throw in a cool terrain and/or hazard to spice things up. Some of the best fights we had from the published adventures where ones with pillars or something that would mess with the group while otherwise engaged in combat. Although without a big list to draw from I'm running the risk of re-using some ideas and I dont want them to get old hat. I'm going to throw in some ideas here and see if anyone else can add to it:
Pillar of Healing - heals all enemies within 5 squares of it 5hp/round. I used this during an undead encounter with a lot of skeletal minions that kept popping back up after the PCs wiped them out until the figured out they had to take out the pillar if they wanted to get out alive.
River or stream - a 15 foot wide stream that was difficult terrain that divided up the PCs. Made it hard to get to the first monsters and allowed a carrion crawler to hide in it and attack a ranger who normally like to hang out back. Very fun encounter.
Deathtrap Sarcophagus - this was from either Dragon or Dungeon Magazine. It basically grabbed and trapped a PC inside of it until it can either be destroyed or lock picked by someone with thievery. Again made the fight interesting as our warlock, who is very tough to take out, was trapped inside while the rest of the party got stuck dealing with the monsters outside of it.