The best reference work about greasing pans that we know is Shirley O. Corriher's CookWise: The Hows & Whys of Successful Cooking with Over 230 Great-Tasting Recipes (William Morrow, 1997).

Shirley discusses pan-greasing in three different situations, for cookies, for foam cakes, and for shortened cakes, and she also discusses double-greasing (butter chilled hard, followed by oil).

If you're planning on doing serious baking, go out and buy yourself a copy of the book on the double. (It also has information about many other cooking processes, illustrative and tasty recipes, and the sober, cheerful tone of one who's been there and lived to tell the tale.) Here's an interview with Shirley; you'll want to have her for your friend.)

Besides butter and oil, Shirley likes non-stick spray.

Margaret also likes spray, specifically Pam spray.   

Mary-Claire likes greasing pans with Benecol Light and when a dessert recipe calls for greasing and flouring she greases and sugars instead.