Musipedia: search music by whistling
With Musipedia you can use this applet to translate the whistle into Pasons Code and search the database for matching tunes.
Parsons Code is a neat way of encoding melodies:
Each pair of consecutive notes is coded as “U” (”up”) if the second note is higher than the first note, “R” (”repeat”) if the pitches are equal, and “D” (”down”) otherwise. Rhythm is completely ignored. Thus, the first theme from Beethoven’s 8th symphony that is shown above would be coded DUUDDDURDRUUUU. Note that the first note of any tune is used only as a reference point and does not show up explicitly in the Parsons code. You can enter an asterisk (*) in the Parsons code field for the first note.
If that’s not your thing, you can just use this keyboard for entering your tune.
I wonder if it can find Cage’s 4′33″