I like G. Moto's idea of zombies, as he an I have had many conversations around mill decks and zombie decks. Some mill the opponent (
Geralf's Mindcrusher,
Rotcrown Ghoul; some self mill (
Armored Skaab,
Crow of Dark Tidings,
Forgotten Creation, etc...). While self mill types tend can be a bit of a concern as to whether you are hurting yourself, try adding
Psychic Spiral. This shuffles your graveyard back into your library, and then mills the opponent for the # of cards you just returned from your graveyard to your library. I like to have that card handy in SB for my black/blue zombie decks when playing against mill decks that use creatures like Nightholwer, Consuming Abberation, etc... because I can quickly get the cards I need from my library to my graveyard (either through my own creatures or through their spells), and either return them from my grave to hand, grave to battlefield, or leave them there if they aren't critical to my combos. Then when they swing with their big, buffed up critter that is taking advantage of the creature cards in your graveyard, throw down
Psychic Spiral and *poof*, that big bad creature is now a bug to be squashed. Preferably with an army of zombies at your disposal.