Popup Window for Email Opt-in

I’m finding it surprisingly difficult to find a good plugin or hack for any type of pop up window. I want to use it for email opt in. Aweber has a good one, but I’m not with them right now. Why is this so difficult to find? It seems like there should be a million of them!

Anyway, I’m familiar with wordpress popup scheduler, but I’ve had a lot of problems in IE, and this plugin also admits it does not function if you’re using supercache, which I consider a must.

Is there anything out there?