For muffins why not use those new silicone bakeware products? You can't use silicone stuff on the stove but you can get the inserts to use on the cookie sheets. They make bread pans out of silicone.

They mean less fat needed because they won't stick.

http://www.noveltybin.com/Product.asp?PID=40015

Scroll down for an article on silicone bakeware. But this site mentions other materials and what you need to look for when buying them.

http://www.dld123.com/q&a/index.php?category=Food