I have read two pretty cluey posters on another site claim Rafa Marquez stacked on 23 pounds for one of his bantam fights...but I could never confirm it. Sam Soliman dropped a pound I think between the weigh in and fight time for the Winky bout.
De La Hoya went from 147 to 145 in the Pacquiao fight I think, same loss as Ruiz. Anyway, the biggest gain is Joshua Clottey in the Corrales fight, weighed in at 147 and was 166 in the ring, 19lbs for a welterweight is insane.
Danny Romero would put on alot of weight early on when he was a flywieght 10-12 lbs for a 112 lb guy is pretty impresive.
Manny Pacquiao jumped straight from 112lbs to 122lbs (in 3 months), bypassing the classes in between, so towards the end of his time at 112lbs I'm guessing he was ballooning up pretty substantially.
Arce jumped up 3-4 weight classes against Cob Castro I think it was. He passed out right after the weigh in.