High level Modules

[Treebore]

The lower levels of Rappan Athuk can crush them. You can also easily power up the Bonegarden to challenge them. The same can be said of Caverns of Thracia. Goodman has several higher level modules that you could turn into good challenges for your party. So does Monkey God.

If you want an old school dungeon Gygax's Necropolis will give you plenty of ways to kill the PC's. Parts of it makes Tomb of Horrors look like a walk through a garden. There are some good pointers for DMing this one on the Necromancer Message Boards in the forum dedicated to Necropolis.

 

[Dannyalcatraz]

Necropolis gets a vote, as does Tomb of Horrors.

Judges Guild Modules tend to be well written, and their high level stuff is pretty good, as I recall.

 

[Blackthorne]

Get your hands on "Glacier Season" in Dungeon Magazine No. 87. Although it reads "for 15th-level-characters", it should be able to handle your party as well.

 

[Dirt]

Hey Fathead, who ran that for you?

I think I have seen that module floating around. I may be able to use it.

Check the Kenzer boards. I answered your PM there too.

I played the Crypt at the Dungeon Crawl Classics tournament at GenCon this last year. I will say this for Goodman Games - they have some excellent and very engaging GMs running their events.