Interesting thing...Calorie Queen actually got IN when Matter Eater-Lad was drafted into the Bismolian senate...and was never seen again, until Giffen's run, where she was Tenz's assistant.
Some more vengeful rejects:
Several of the original lineup (chronologically, not in order of appearance) of the Legion of Super-Villains were rejects...Spider Girl, Radiation Roy...Ron-Karr... Then Esper Lass, Micro Lad, Nemesis Kid, and a couple others. (Including some real losers like Eyefull Ethel and Tusker - who was briefly a member when the Legion was hijacked by Dynamo Kid.)
In the original continuity, Spider Girl also eventually joined the Legion, though most of her tenure was on the run under a new code name (Wave, the same name she uses in the Legion cartoon).
Jungle King AKA...ugh...been a while...I think he changed his name to Monster Master, or something like that... Anyway, he's one of the few who came back for revenge in the same story where he was rejected.
The entire JLEarth from the recent Superman and the Legion arc is made up of rejects - Radiation Roy, Spider Girl and Tusker again, Golden Boy, Storm Lad, Absorbency Boy (now going by Earth-Man). I'm not sure if Ethel was an actual member, or just an ally.