You can base your search on melody (i. e., pitch and rhythm), melodic contour, or just rhythm.
Identify a melody by entering it
If you are unsure about the exact intervals between notes, try the Melodic Contour Search. This way, all you need to know is whether the tune goes up, down, or if the pitch stays the same.
For an even simpler (but less specific) way of searching, try the Rhythm-based "Query by Tapping" search method.
If you are a computer, or want to integrate the Musipedia search into your own web service, you can use the SOAP interface, which makes it possible to search based on melody, contour, or rhythm.