Chiswick Marketing Gary Halbert was one of the best copywriters ever. He has a great site, now run by his family that gives away all his secrets. Go here and then scroll to the bottom and read the Newsletter Archive.
This is a video of him in 2004 about a year before he died talking about the motivation to write good copy. A very funny guy and his writing is fantastic.
[youtube=http://www.youtube.com/watch?v=KEyG-5R5prw&hl=en&fs=1&rel=0&color1=0x006699&color2=0x54abd6]