On April 1 we will hear countertenor David Daniels sing Giulio Cesare at the Met. 
Handel wrote absolutely exquisite music for countertenor voices. Here's a gorgeous example, sung by Iestyn Davies:

http://www.youtube.com/watch?v=is9vRFUgk_k

You can read about the recent renaissance in countertenor singing here.

And this is Daniels in a stunning duet from Giulio Cesare:

http://www.youtube.com/watch?v=m8byfaTlsYI