Kim Witman, as she makes the rounds of the Wolf Trap Opera audition tour, has been faithfully recording the arias that singers have been offering each year, and here are the most popular arias of the 2006 version of the list:
Ach ich fuhl's (30x)
Sein wir wieder gut (19x each, tied)
Va! laisse couler mes larmes
I know a bank (5x)
Dies Bildnis (27x)
Hai già vinta la causa (30x)
Catalogue Aria (8x)
While reading the entire list won't tell you what the most successful singers are auditioning with, it will tell you what the overall trends are in terms of aria selection, as well as being a springboard to finding some new and ineresting audition-worthy material.
Also of interest on the Wolf Trap blog is the list of most popular opening arias.