Whenever I DM, my favorite trap is almost always the pit trap. It's classic, it's versatile, and it can be triggered a thousand different ways.
The pit trap is easy to make interesting and deadly, even at higher levels. At low levels, it's pretty common to just have a straight ten-foot-deep pit with a solid stone floor. It does some damage, but it's usually pretty easy to get out of it if the party is carrying rope (and really, what self-respecting adventurer doesn't carry rope?). At higher levels though, the pit can have spikes at the bottom for extra damage, it can be deeper, or it can have something waiting in it.
My favorite pit trap for high-level parties is to have a pit trap with greased walls and a pit of acid ten-feet down. It's tough to get out of something like that. Or, even better, have it be a regular pit with walls angled so that the pit is wider at the bottom than at the top (to prevent climbing) and have a family of monsters living down there (carrion crawlers, wolves, dire rats, anything like that). Or, go with a classic monster and have the adventurers fall directly on top of (and into) a gelatinous cube.