Many of you might have trouble with this one; some might not be able to choose just three and some might not like any provision from this band.
Although many albums exist, I could ignore them all except for these four :

Court of the Crimson King -- Larks Tounges in Aspic -- Starless and Bible Black -- Red

My top three songs could easily come from the debut album :
I Talk To The Wind
Epitaph
Court of the Crimson King

But I also love STARLESS from the Red album.

Those four songs, and certainly those four albums IMO, create the best example of classic KC.