I don't have any favorite PSD. It depends on the type of cover I'm making. But here are some that might be helpful. All can be found on Deviantart.com. I do not own these.

http://ravenorlov.deviantart.com/art/PSD-24-506230622

http://soclosepsd.deviantart.com/art/PSD-O31-Vintage-334804946

http://seolilihyun.deviantart.com/art/PSD-7-Brown-and-Blue-373286409

http://www.deviantart.com/art/PSD-47-362940629

http://www.deviantart.com/art/PSD-34-348737392

http://www.deviantart.com/art/PSD-22-Dead-Autumn-346559385