Tiny speakers, used in headphones - what are these called?
Added:

For components try searching for "speaker" and sort by size.

In Digikey's catalog "speaker" will get you this and after you reject the expensive tiny specialist units you get eg.

These 

Drawing low on dimensions.
 A few here
  Allegedly 13mm x 2mm. 

http://www.puiaudio.com/pdf/AS01308MR-R.pdf



Or these - prices  and datasheet.  

From 13 mm dia



http://www.mallory-sonalert.com/Articles/TechAppGuides/Miniature%20Speaker%20Models.pdf
  http://search.digikey.com/us/en/products/PSR-11N08S-JQ/458-1119-ND/2071435



Earpiece.
 Magnetic earpiece (some)(mot common)
 Piezeoelectric earpiece (some)

Many but not all of these will be relevant, with links - via Magnetic earpiece



and Piezoelectric earpiece