Whizbang Dustyboots
Gnometown Hero
Van Richten's Guides would be my suggestion, most of which have some interesting ideas that can easily be adapted to your game of choice.
The question for me is: did anyone buy and use Masque of the Red Death back in the day, and how was it?

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.