the elements of moral philosophy by james rachels....it was "suggested reading" by my med ethics teacher so i didn't read all of it due to lack of time, but it reads very easily, i found what little i read to be very engaging, and he's always coming out with updated editions to keep in time with the changing demands of medical ethical issues...my impression of the book is that it's a classic with regards to medical ethical literature
also, i had to read a great deal of Steinbock & Arras' Ethical Issues in Modern Medicine that drinklord suggested, but it definitely reads more like a textbook....i found some articles interesting but others absolutely terrible to read...but then that's what you get a lot of the time in philosophy....it seems like that's another good resource to have if you're really into this stuff, but i suggest the james rachels if you're looking for something easier and more enjoyable to read...plus, it isn't a textbook, or else it doesn't feel like one
