Can't Be Tamed
(Who Owns My Heart WW and not only this selected European countries, not even including the UK, **** HWR did)
Two More Lonely People
Stay
Robot
Although Katy has songs from each era that could've been singles and weren't, the ones that stick out for me the most are Hummingbird Heartbeat and Walking On Air. Honourable mentions go to Legendary Lovers, Peacock and If You Can Afford Me.