I think my favorite Q episode is the one where he loses his powers and chooses human form (aboard the Enterprise of course) to live out his now-mortal days.
Towards the end, Corbin Bernson shows up and DeLancie's character sees him and goes "Q!" and Corbin Bernson is like "Hey Q" and I think this is the first time we realize that there are other Q and they just call each other "Q" because they're all Q, of the Q Continuum. Turns out Bernson/Q is the one who got DeLancie/Q kicked out, but after some chat, Bernson/Q kinda shrugs and says "Okay... you got your powers back." Immortality, omnipotence, everything, but to them it's like resetting your password or something. No biggie, don't do it again, later.