Nightfall
Sage of the Scarred Lands
Well I believe that Necropolis will definately be high level, starting at 10th and ending near 19th I believe. That's by Necromancer Games as well. Another is probably the best d20 dungeon crawl I can think of, barring of course Return to the Temple of Elemental Evil, Rappen Athuk. 15 levels of pure unadultared hell. Believe me, while a high level party MIGHT get through levels 1-6, 7-11 are TOUGH!