Think Tank, VOY 5
A shocking turn of events! Despite the embarrassing presence of Jason Alexander (who is so awful that I honestly thought I’d be unable to watch this episode) the writing behind this one is so strong you can overlook him sucking up the joint.
A floating (in subspace!) think tank that will aid ships (or cultures) in distress for a price. . . featuring all sorts of floating plasma and robotic intelligence. Toss in some bounty hunters and story reversals and you have yourself a good show. If they got someone other than Costanza, it would be close to perfect.