Please submit encounters - either generic, stand-alone, or part of an ongoing scenario (but please modify it so that it's actually useful out of context) - that involve action. That is, include a major action element: small group combat, angry monster combat, battle, traps, danger, athletics, pursuit, etc. D&D does some of these very well; others poorly.
Begin your idea with the edition of D&D you're using if it matters (e.g. if you're using stats) and what levels the encounter is intended for (more power to you if you can make it scalable). If you can include stat blocks for combatants, DCs for skill checks, and page references in rulebooks, that's all the better because if this works right, we'll all use the results.
Oh, and if you're writing action scenes all the time (say, because you DM a D&D game :P), you could just copy-paste-post one of your favorites; you don't have to do any work except for cutting it to comment-length (or parsing it into comment-length sections).
I chose to specify action scene ideas because they're easier to describe in D&D. I figure in a day or two we'll have a lot of neat suggestions that the DMs and future DMs among us can go back to for inspiration or seeds for random encounters or even important action scenes.