While a flanger pedal can be used for many different instrumants (including vocals), they are most commonly used for guitar. The flanger sound can be either extreme or subtle. On the extreme end, they can sound like a swooping jet airplane or eben a runaway train (listen to Van Halen II for examples).

 

On the more subtle side, flanger pedals can create a lightly swirling effect that is good for both chords and solos. In the right hands, a flanger can even replicate the twirling sound of a Leslie Rotary cabnet as used by Stevie Ray Vaughn and others.

 

Vintage and boutique flanger pedals are in great demand right now, and they can command outrageous prices sometimes. But if you do some searching, you can often pick one up cheap on an eBay auction, even the classic models from the 70s.