The Doctor's Theme
From Tardis Wiki, the free Doctor Who reference
"The Doctor's Theme" is a piece of music composed by Murray Gold which served as the main musical motif for the Ninth and Tenth Doctors. It first appeared in the 2005 episode Rose. In Series 3, it was somewhat superseded by "The Doctor Forever", but returned in a new arrangement for Series 4. The signature notes from "The Doctor's Theme" are heard as part of "Vale Decem" immediately after the Tenth Doctor speaks his final words in The End of Time.
In the era of the Eleventh Doctor (Series 5 onwards), "The Doctor's Theme" has been replaced by "I Am the Doctor".