Well, I think such a list would tend to weight towards higher level spells as a matter of course, as such a level of play is more rare. Also, some of the world building/plot based spells may appear more frequently. Come to think of it, is the question more along the lines of "never seen the PC's cast?" or just never seen utilized in in game period?
Imprisonment and Sequester are two that I have never personally seen cast, though they are both rife with plot and adventure potential (someone, maybe even the PCs, need to release a long ago Imprisoned archmage/Demon/King, or accidentally trigger the condition to awaken the princess/vampire/whatever).
I don't think I've ever seen Mirage Arcane or Programmed Illusion cast either.