Placebo is currently in the midst of co-headlining a U.S. tour with Stabbing Westward, and on Monday night in New York City, the Brit-based trio was joined onstage by a surprise guest -- David Bowie.During the encore of Placebo's set, Bowie came onstage and lent vocals to "Without You I'm Nothing," the title track from the group's most recent album. The two then romped through a cover of T. Rex's "20th Century Boy," a track Placebo recorded for the soundtrack to "Velvet Goldmine," a film based loosely on Bowie's glam-era career. As we previously reported (see "Placebo On The Importance Of Being Bowie"), Bowie has taken an active interest in Placebo since he heard some of the band's demos a few years back, and even invited the trio to open for him on a few dates of his 1996 European tour. Just last month, Bowie and Placebo performed "20th Century Boy" at the London Arena during the 1999 Brit Awards, U.K.'s equivalent of the Grammy Awards. The Placebo-Stabbing Westward tour is scheduled to roll into Cleveland's Odeon Club tonight and the Clutch Cargo in Pontiac, Michigan on Friday.