(interj.) A portmanteau of "wow" and "cowabunga". Used to express one's reaction to something that is both surprising and awesome.
David Bowman - "Oh my god, it's full of stars."
HAL - "Wowabunga homie!"
World of Warcraft junkie - "I gave up WoW because it was ruining my life..."
Rest of the world - "Wowabunga!!"