http://www.onlinepianist.com here you can learn songs. The site has three different level of difficulty. Its free and you can slow down the tempo/speed, watch the notes on the piano, choose to see only one hand (left or right) or both at the same time. There is a premium edition for extra features but they are not necessary I guess.
There are a lot of popular songs that have piano music. Bruno mars is popular as well as Alicia keys for the more modern stuff. Try going to your local music store- they will have the best idea of what music ur looking for and if u find a good shop they will have mountains of sheet music at ridiculously awesome prices.
"Imagine" by John Lennon. I'm not a pianist, but I can play that one. All white keys! Most British pop ballads have that thing where it goes: RH chord-LH bass note like in "Imagine." You can play around with chords and come up with your own songs that way.