Comb Duck/

Knob-billed Duck

Sarkidiornis melanotos

Photos have been downgraded in size and quality for the Internet.
Comb Duck Comb Duck male

The unusual Comb drake with comb. The Comb Duck has two sub-species: Sarkidiornis melanotos melanotos (above/immediately below) which has grey flanks and comes from sub-Saharan Africa and tropical Asia and Sarkidiornis melanotos sylvicola (further below) which has black flanks and comes from tropical South America.
Comb Duck Comb Duck female

Comb duck (female doesn't have comb on bill)
Comb Duck male Comb Duck

In the sunlight the Comb Duck's plumage shows beautiful iridescence
 

Putting tongue out