Finding Sheet Music

• Sheet Music Plus: I use this site to order printed music 
• Music Notes: I go to this site if I want to purchase sheet music that I can print right away 
  
• Hennepin County Library: Surprisingly, the library has a nice collection of all kinds of sheet music. I usually check here first to see if they have what I'm looking for. Once you have a list of search results, you can filter them by limiting the format to "printed music." 
  
• International Music Score Library Project: If I'm looking for an older classical piece I usually go here first. This website has a huge collection of mostly classical music that is no longer under copyright and can be used by anyone for free. The music exists as PDFs and can be downloaded and printed. It may take a little searching to find exactly what you're looking for. Not everything you find may be available in the US as this is an international library. 
• Sometimes I like to go to an actual music store. I would recommend Schmitt Music or Groth Music. Both have large selections of piano music and pianos to try it out on!