DIAMOND/PEARL/PLATINUM spots:
You can surf at the Resort Area and find Psyduck (1 EV) or Golduck (2 EVs). Another place is the Old Chateau, where it is 100% Gastly (1 EV) or, if you have a GBA game, Haunter (2 EVs) as you walk around.
HEARTGOLD/SOULSILVER spots:
Surf in Ilex Forest to find Psyduck (1 EV) and Golduck (2 EVs).