[sdiy] rare parts

[Mrs. Rectangular]

one of my friends who i had not seen for a while has a large collection of rare electronic components. while he was showing off his collection to me he asked if there was anything specific that i wanted. he has lots of ICs, transistors, diodes, capaciters.....
so i thought i would ask everybody here. 
what would be some of the most awesome rare components that would allow me to build synth modules that would otherwise be unbuildable?