I bought this one...
http://www.bestbuy.com/site/wd-my-pa...?skuId=5605521
I actually purchased the 2 TB white version because it was on sale as a My Best Buy member early access deal for 80 dollars (down from 90), but you could get the 1 TB red version for 55 if looking to just bump over the 100 dollar mark.
Also I just want to clarify that I purchased the external hard drive to use with my Xbox One. I don't think PS4 currently allows for external hard drive support. To my knowledge you have to change the internal hard drive to upgrade the storage capacity of the PS4 (although I do believe support for external hard drives is rumored to be coming soon). Someone please correct me if I'm wrong.