for a bundt pan, the best thing is to use a cooking spray, because that'll get into all the nooks and crannies.

If that's not working, you may wish to consider also flouring the pan. Grease it, sprinkle in some flour and shake it all around until evenly and lightly coated, throw away extra. If you're worried about using flour b/c you don't want your cake covered in flour at the end, use powdered sugar.