I've done a shameful 13:
Bat, Canada's Wonderland
Boomerang, Knotts Berry Farm
Boomerang, Pleasure Island
Boomerang, Bellewaerde Park
Boomerang, Wiener Prater
Boomerang Coast to Coaster, Six Flags Discovery Kingdom
Boomerang Coast to Coaster, Darien Lake
Flashback, Six Flags New England
La Via Volta, Walibi World
Sea Serpant, Morey's Piers
Sidewinder, HersheyPark
Wipeout, Pleasurewood Hills
Zoomerang, Lake Compounce
and the winner is....
The one at Prater, purely for the fact that it has lap bars.