If we're talking modules over 14th level, there are a few that were done decently:
H2 The Mines of Bloodstone is for levels 16-18 and does a pretty good job of challenging high level characters. There are some bits that were a little contrived for my tastes, such as the "Tests of Orcus" portion of the adventure, but overall a fun module. It's sequel, H4 The Throne of Bloodstone, on the other hand...
WG6 Isle of the Ape says for levels 18 and up, but anything over 14 will do. Yeah, it's got its share of faults like the heavy spell restrictions, but I found it does a good job of presenting a self-contained high level adventure that isn't an "end of the world" scenario. But I'm a big King Kong fan, so YMMV.
The Lich Queen's Beloved from Dungeon Magazine #100 is for level 18 and up. It's the only 3e high level module I'd include on this list. There were a lot of epic level adventures published for 3/3.5 and many of them are good, but frankly, the bloated epic rules system turned things into power gaming silliness. I liked the The Lich Queen's Beloved for doing an excellent job of portraying the githyanki world and presenting a pretty great villain. With some effort to tone things down and remove some of the epic rules craziness, it would be worthwhile converting to 5e for those looking for a high level module.