It seems to me that not too long ago, there was a superlative card called Necropotence. Then, they neglected to reprint it in 6th edition. Still, you have a couple of options.
Greed - 6th edition card, a mainstay since the beginning days of Magic. The problem is, you need to spend 2 life and BB for every card you draw. Use this only if you have a deck based around the theme of draining life or gaining it.
Jayemdae Tome - 6th ed. Classic card drawing engine that's good if you have some extra mana.
Howling Mine - Excellent so long as your deck is designed to be fast and furious, meaning you'll get more use out of your extra cards than your opponent will. It's a risk card. It's virtual suicide if you're up against green.
Yawgmoth's Bargain - Urza Block. Very rare, hard to obtain, universally hated and just as irritating as Necropotence, if not more so. This is the best Type 2 card-drawing engine for black. The biggest catch is that in a month, this won't be Type 2 legal anymore. Sorry. Those are the breaks if you're going to succumb to the Type 2 format.
Grafted Skullcap - Urza Block. Again, if your deck is designed to expend it s cards in the shortest amount of time, this is actually better than Howling Mine. Unfortunately, like the Bargain, this is going away from Type 2 in a few weeks.
My advice? If you want to stick to Type 2, wait patiently for Invasion. Hopefully, you'll get something juicy in that set. Getting card-drawers like Bargain would be a waste of money this close to the next set cycling.
