http://cockatrice.de/

I stumbled across this program last week and I've been playing quite a few EDH games with it. It takes a few games to understand the interface and the "unwritten rules" of how to use it, but after a few days it was second nature.

If you do end up trying it out, post your username here.

My username is "Toxygene".

Signed up. Played my first EDH game. Got stomped.

Name: negativeview

tilzinger is my handle

I registered - surrealwebs

Here's a good quick way to get up and running for an EDH deck:
http://forums.mtgsalvation.com/showthread.php?t=442195