mmadsen, I've been observing this thread, and if this keeps growing as it does, you should make a netbook or something. This is just that good a thread!
Thanks for the kind words, Arthur Tealeaf!
Wizards can only be specialist wizards and can only cast spells from their schools (+ universal spells). Ofcourse you can multiclass into other specialist wizards (eg. level 10 diviner, level 4 evoker). This makes the different types of wizard more distinct, and now necromancers really are the masters of necromancy!
An excellent suggestion...that's already on the list.

Yeah, I know, the list is getting a little unwieldly!
Have a campaign where orcs or kobolds or some of the other "lowly" races rule over the other races...
Good. I think Rune mentioned finally having a campaign where he takes Halflings seriously; they rule the skies -- and thus a large mercantile empire -- from their airships.
EVERY mythical or unnatural monster has a special weakness... just like vampires who can't stand sunlight or running water and norwegian trolls "pop" in the sunlight. The raksasha can't take blessed crossbow bolts, so maybe a balor demon dies if it gets pure silver in it's eyes; Beholders take great damage from salt in its central eye; Black unicorns can't take the dust from the crushed horn of a unicorn; Maybe evil fey can't stand the ring of pure silver bells.
I strongly endorse this one. As I said before, I much prefer DR with a weakness of silver, or mistletoe, or salt, or whatever to "+3 or better magical weapons".
Another option is to grant Improved Critical to anyone who knows the monster's weakness. "The dragon has a weak spot in his soft underbelly, to the right..."
"Every monster has a purpose: No "natural" monsters. Orcs exist to kill good creatures; the "Black Knights" all exist to combat a specific god; Basilisks are created by the god of stone to punish those who doesn't appreciate stone by turning them into it; and so on...
This might also be combined with the "every monster has a weakness with good effect. For example, the "Black Knights" can't stand the name of the god they combat spoken out loud.
I like this. It flies in the face of the not-at-all-fantasy style of most modern games, where every race just sort of sprang up along the way.
Eliminate monsters, and have the planet itself be the enemy. Safe areas exist, and this is where good races stay. When moving on evil ground, the planet itself attacks, by manipulating and controlling every aspect of nature. Maybe the whole campaign could be centered around stopping this curse?
This reminds me of a different idea, one that's neglected in most games even though it's at the heart of much fantasy fiction. In games, sorcerers generally cast spells that a powerful in some ways but very limited in scope. In literature, the Dark Lord turns his kingdom black under perpetual night, the White Witch blankets the land in perpetual winter, etc. Allow meta-magic (or some other mechanic) to vastly increase the size and duration of thematic spells.
(Someone once mentioned a Dark Sun supplement, Dragon Kings, that had 10th-level spells that enchanted an entire army's weapons, etc. That's what we're going for.)
Let the characters play the villains, plotting to take over the world and controlling their evil armies. Let them fight of bands of adventurers trying to stop their reign of terror. Afterwards, let them play adventurers taking on the villains they played earlier.
An old standby, but I like it -- and it belongs on the list.