Coolest rainbows I have seen were around Grinnell Glacier in Montana. They make arches over mountain peaks, and connect mountain peaks together and the like, pretty neat stuff. Got caught in several downpours around that area, and by downpour I mean the air turned into water, rained so hard we couldn't do anything but laugh hysterically and scream like madmen/madwomen.. But afterwards saw some pretty cool rainbows..

edit: think my license is revoked in Montana

Found an example online