I saw a guy w/ a card in his Elf deck from Onslought last night that caused you to discard his hand to draw a card for every creature in play...toward the end I was hoping he'd use it...
-Ferret
"Fifteen Elves + about ten insect tokens = instant win for Ferret!"
Slate of Ancestry is nice for the bigger tribal creature types - dragons, beasts, that kind of stuff... For the smaller ones - unless you have some mana heavy spells, you should be able to hard-cast everything...