In 4E making interesting encounters is primarily about running them in a diverse, unique, and interesting environment...
Completely agreed. I've found environments to be the most memorable part of battles, but it's also by far the hardest to generate, due to the lack of tools.
There is a tiny selection of traps and hazards in the DMG, but even if it were fuller, traps/hazards alone don't necessarily make an interesting battleground. It's also really hard to predict how different environments will effect the challenge rating of the fight (sometimes the party has found cleverer ways to use the terrain than I have, sometimes it's just been to the advantage of my baddies).
I've included several fun backdrops so far, but I still wish there were some dedicated guide to creating a wide variety of maps in a more or less formulaic or random way, for those nights when I'm throwing an extra encounter or two together at the last minute.