Free Public Domain Pictures

Finding great pictures you can use for free is hard, here are some links I've compiled from some site my friends have sent me. Please be aware to always read the conditions before using the pictures.

Private Sites:
Stock.Xchng - One of the best place to get good photos on almost anything.
Morguefile - A perosonal site offering tons of beautiful photos.

Government Sites:
Nasa - multimedia archive search.
Nasa Space Gallery - Tons of amazing pictures.
National parks - Gallery of US National Parks.