I'm not so much looking for stuff where an effect was used here or there, but where the effect is on prominent display in the song; nearly a "hook" in its own right.
Tommy James & The Shondells - Crimson and Clover (for the extensive use of tremolo... bonus points for the fuzzed out solo, wah wah, etc.)
The Small Faces - Itchycoo Park (semi-early recorded example of flanging - comes in at about 0:50)
Sweet - Love Is Like Oxygen (auto panning at 3:21)
Okay, admittedly, the last two don't feature the effects as prominently as they are on the first example, but that's where you guys come in. What are some of your favorite songs that have used effects in a significant / dramatic way?