Searchable Database of works with extended techniques for flute, alto flute, bass flute and piccolo, created by Matthias Ziegler and Shanna Gutierrez: FluteXpansions
(all material from my old list, and much more, can be found here.)
This site also has demonstration materials on extended techniques.
Here is a shorter, printable list, divided into grades of easy, moderate, difficult and very difficult. These works are for flute only.
Repertoire with Extended Techniques Shortlist (for easy access and handout)