Amazon.com. I wouldn't trust eBay or any other 3rd party retailer.
Ive had excellent experiences with some established ebay sellers who specialize in selling applecare very cheap. not sure if that has changed, I got mine about 2.5 years ago.
http://www.bhphotovideo.com/c/product/582539-REG/Apple_MD010LL_A_3_Year_AppleCare_for_Mac.html
legit seller for apple 104
Apple itself is good if you qualify for an educational discount.