I recently did some digging and found a number of sites that specialize in providing free popular piano sheet music for my daughter. She is learning to play the piano and rather than plunk through "boring old" music she wants to try to learn to play more recent popular piano pieces. The selection of pieces at each of these sites is hit and miss, but if you look around you can find almost any current piece of popular piano sheet music and download or print it directly from their site.
If you have problems finding the music you want using these sites please check out the sheet music search box at the bottom of the article. Please note that all of these arrangements appear to be transcriptions done by independent authors.
This very extensive site is filled with free piano music sheets for just about every current popular artist and lots of movies as well. Katy Perry has six of her more popular songs on the site, as do Justin Bieber, Coldplay, and hundreds more. They are pretty ad heavy on the site, with several places to click that look logical but turn out to be well crafted ads instead. On the individual detail page for the song you want look for a link marked Show Piano Docs and this will take you to a visual view of the piano music you can download.
Words3Music does not have nearly the same size of collection as PianoDocs but they do have a respectable amount. Organized into four categories all of the music on the site is collected either by artist name, the title of a movie or television show, or the name of a piece of Christian music. Most of the files also include access to a MIDI file which makes me think that some of them might be being created directly from the MIDI file itself. Clicking on the download link at the bottom of the page will take you to Scribd.com to complete the final download or print job.
Of all of the sites mentioned Pianotte is the one that makes it easiest to get to the free piano music sheets without a lot of garbage on the screen. Yes, there are ads in the sidebars but the center column where the information is is relatively clean and easy to read. Lots of good free popular stuff here arranged by title though instead of by artist.
Weebly's sheet music page is a pretty bare bones site but with a LONG list of titles of popular music, movie and tv tunes, jazz, and even Christmas sheet music. No ads really, and easy to find stuff with a simple Cntrl-F search.
If you are tired of searching manually through the sites shown above give this custom Google search engine a try. Simply enter in the title or artist of the sheet music you are looking for and it will search through these sites (and more) and return any matches that it finds.