Playing Piano by ear?

I have been playing Piano for 20 years and can play just about
anything that it put in front of me but I can not for the life of me
play songs by ear or play a tune with out sheet music. How can I work
on this? People always expect me to be able to play all of these
popular songs that I know, but I just can't seem to be able to play
them by ear. Any suggestions?

DREW