I like words, especially pairs of related or/id words:

algor   algid
calor   calid (obs.)
candor  candid
fervor  fervid
fetor   fetid (or fœtor/fœtid)
fulgor  fulgid
horror  horrid
humor   humid
languor languid
liquor  liquid
mucor   mucid
pallor  pallid
rancor  rancid
rigor   rigid
sapor   sapid
sordor  sordid
splendor    splendid
squalor squalid
stupor  stupid
tepor   tepid
torpor  torpid
tumor   tumid
valor   valid
vapor   vapid