I've been eyeing Card Kingdom's battle decks. They're 60-card decks put together from inexpensive singles (most worth less than a quarter) around some theme, like goblin generation or enchanted creatures or recycling your graveyard or whatever.

Each deck is only $10 so you can pick up a handful of them and play them against each other with friends. They're not intended to conform to any particular format, but they are supposed to be relatively balanced against each other.

I heartily second EDH, it's great.

My friends and I would often play a hybrid of EDH and 2HG (Two headed Dragon?), it was a real good time.