This is a mono-black infect standard legal deck I made;
2 Flesh-Eater Imp
2 Hand of the Praetors
4 Plague Stinger
3 Septic Rats
2 Ichor Rats
2 Contagious Nim
4 Vampire's Bite
4 Virulent Swipe
4 Demonic Appetite
4 Unholy Strength
4 Tainted Strike or 4 Mutagenic Growth
The Tainted Strikes can be replaced with Mutagenic Growth to make it more effective but no longer mono-black.
The main plan is to just summon creatures quickly then attack with them, when one gets though throw any instant cards you have on it to buff it.
The fastest it can do is turn 3, generally using Plague Stinger with 3 Vampire's Bites to make it a 10/10 flying infect.
This deck won't really work well in games that drag on too long, also may have problems with weenie decks due to very little removal, but as long as you can get in there quick enough it's a fast and silly deck.
I was dissapointed at the lack of black buff cards in NPH though, and hope that M12 will introduce some new ones or at least reprint the good ones since a few cards no longer be standard legal once M12 is released.
Got any thoughts or questions? Post in the comments.