I thought these were interesting, particularly because of the large change in meaning by a single letter.
quob = to throb; to quiver
quod = prison
quop = to writhe; to pulsate; to undulate
quiz = absurd person or thing
I also liked quisquos, which Phrontistery says means perplexing or difficult to deal with, while Logophilius defines it as baffling, perplexing.