I was listening to the recent Datanauts podcast, part of the Packet Pushers family. They did a whole podcast on conferences. It was a good listen, especially if you haven't been to many conferences and you're interested in attending but don't know which one to attend. One thing I've personally always struggled with is finding out about new conferences that are likely a little smaller than your typical EMC World, VMWorld, and Cisco Lives.
One site Chris Wahl mentioned was lanyrd.com. I created an account and it's not a bad little site. It looks like it's been bought by EventBrite, so you can merge it with that account if you already have one. Its a bit disorganized, but I don't know of any others out there. So, if you know of any, reach out via the comments and let us all know!