I'm really excited to replay the Blackguard modules. A great 3 part story loaded with evil as you progress down the path of a blackguard. I still can't forget the part where you're trying to revive a skeletal dragon, and it requires the sacrifice of a bunch of innocents, but where could you find so many innocents? Oh, right, the school
The twilight/midnight modules were some pretty fun modules, as well, for the goody goody paladins.
Out of the original set, HOTU had one of my favorite high level battles.
You had to defend that keep in the underdark. And hordes of fairly low level enemies come at you, and you just feel so badass tearing through them. But it's an endurance trial, and you have to make sure not blow all your spells and abilities on the weaklings, otherwise the boss as the end of them will slaughter you.