Add to this mix the epic ideas discussed
here
Not all of the epic ideas are epic level handbook-required. In fact, most are not.
Also
- Vermin - not good versus evil or law/chaos but everyone can get behind fighting the giant ants and roaches
- Characteristics for monsters - it might be tough, but roll stats for monsters. There's no reason (expect simplicity and making the DM's job easier) that monsters don't have varied statistics. This includes the base characteristics (STR, CON, etc.), hit points, etc.
- Location-based magical theory. Magic from one place may work completely differently from magical theory in another region. Spellcasters may or may not be able to master both without multiclassing or assigning feats.
- Ritual based magic - few magics would be castable in one action, all others would require much more time
- Alchemy- (or other item-) based magic - most magics are not spontaneously castable and instead must be brewed, enchanted and stored within items
- Enhanced sympathetic magics - you have to eat a spider to spider climb - you can see how the sympathetic link to the magic would be powered. What if you had to eat 100?
- Magical wands and focuses - in order to work magic of certain levels you must have a wand, staff or other magical focus device which may or may not be made specifically for its wielder. Loss of the item impacts ability to perform magic (or prevent it entirely)
- Spellcasting check for magic - in order to cast the spell, any spell, you have to make a concentration check
- No one adventures in the land of Faerie...why is that? Fey PCs dealing with Fey-specific issues