Memo to John Travolta: You should have held on to that white suit you wore 18 years ago in Saturday Night Fever. The outfit has yellowed, and it sure ain't Armani, but those old disco duds are expected to bring between $30,000 and $50,000 at the June 28 auction of film and TV memorabilia at Christie's East in Manhattan. Not bad for polyester—or for critic Gene Siskel, who bought the suit for $2,000 at a charity auction in 1978. "When my friends try it on, they do the pose from the movie, and they smile," says Siskel. "It's magical."

So is the name James Dean. He may be the Rebel Without a Pulse, but his possessions are highly collectible. The Christie's items being sold by a Dean intimate include an unsigned marriage certificate on which Dean is believed to have written the name of his flame, actress Pier Angeli. Packaged with Dean's prayer book, it's expected to bring $3,000 to $5,000.

Who buys this stuff? People like retired British banker David Roberts, 52, who plans to bid on a sequined Marilyn Monroe gown ($20,000-$30,000). "If I don't get it, I'll get Carole Lombard's toothpick," he jokes. No, that's not really on sale—but he can pick up Jean Harlow's powder puff for about $2,000.