MobileSheets is one of the first android based sheet music reader applications available on the market. It allows you to carry your entire sheet music (or guitar tablature) library with you wherever you go. It also enhances the experience by providing features that all musicians can appreciate - annotations, a built-in metronome, music playback from your library, the ability to jump between pages with a single click, and bookmarking. The best part is being able to quickly find the songs you want in seconds. Setting up your sheet music library may take some initial work, but with a free companion application for your PC, typing in the data is a breeze.
Note: Galaxy Tab 7" has various layout issues, and is therefore only partially supported.