It's supposed* to be KILL-oh-metre. It's KILL-o everything else (KILL-o-gram, KILL-o-joule, KILL-o-watt), and the stress pattern is the same for the other prefixed units (CEN-ti-metre, MIL-li-metre, etc.). When I hear kill-AW-metre, I feel like yelling "cen-TIM-etre! mil-LIM-etre! kill-AW-gram!" at the TV. But that's just a personal pet peeve. Looks like the mass media (mostly USn) will change the pronunciation of this one until it becomes the accepted one, over time. Future generations will wonder about this anomaly when saying the names of SI units.