[Found on Stomp Tokyo]
Though I admittedly have little knowledge in the genre of Japanese sci-fi, I do know one thing: when a UFO crashes into the ocean near Tokyo, chances are pretty good that an attack on the city by a giant monster is inherent. Call it intuition.
How about a MMORPG, Exteel. I haven't played it, by IO9 gave it a nice review. Apparently it's more combat than RPG.
[And this, from TVtropes]---
Who needs an Abrams tank when you can have a 100-foot man-shaped robot with a glowing sword and a fist that fires off like a missile? There's no argument - fighting robots are just infinitely cooler than ordinary vehicles. Whatever their shape, though, they are all known as "mecha". The "mecha", or "giant robot", concept is ubiquitous in Japanese pop culture, and is more than adequately represented in anime. Despite the name, the robots need not actually be "giant" - some are merely human-sized, and some even smaller. They range from the boomers and hardsuits of Bubblegum Crisis, to the Tengen Toppa Gurren Lagann big enough to use galaxies as shuriken (no, really!).
Giant Robots Smashing into other Robots.
Needs more smashing!
But maybe they just want to get dome work done.
Coincidence or Copycat? What is the difference between a Giant Robot and a Big Giant Robot anyway? I suppose there is room enough on the internet for the two of us. ;-)
[from Mecha Image of the Day - here]
Finally, here is my kind of Giant Battling Robot from the game Battletech.
So many robots, so little time. Maybe post your favorites here?