Below are links to sheet music resources. Each link will have a description explaining how to download or request free sheet music. I have used all of these resources at one time or another and they are very valuable resources to help you save money, while allowing your musical repitoire to expand. Enjoy!
Pianolicious Blogspot is a great free sheet music resource. The sheet music is organized alphabetically. If you're looking for Coldplay sheet music for example, click the A-C category and then scroll down until you find Coldplay. Note: This website is notorious for pop-ups! Be prepared to close them when they come up. Not every arrangement found on this site has been done by a professional, however everything is free.
4 Shared isn't just for sheet music. It is a file sharing site. You can find books, applications, music, etc. To find sheet music, you should first sign up for an account. Once you have an account you can begin to search for your music by putting in the name of the song or the artist followed by "pdf", e.g. "Coldplay pdf". Once your search results appear click the link on the one you want to download. This takes you to the download page. Click the grey download button below the box showing the document that you want. Don't get distracted by all the other dowload buttons on the page. Once you click this button another page will open with a button that says free download. Click it, wait 20 seconds, and your download will start.
Besides silly videos, Youtube has some great tutorials and free sheet music available. Just type in the song title you're looking for, followed by "piano sheet music", and hit enter. Most Youtube users that share music will have a link in the description for their video. Find the link and get your free music.
This is another great site allowing anyone to download various arrangements of popular hits and some very obscure pieces as well. The best part is that the music is all free!
This site has free sheet music seperated by difficulty levels. Some of the songs are even linked to video tutorials!
This site has free sheet music for classical piano. They also have some violin and piano music.