Well i cant choose one for sure so ill just state 3 or so;
-Mega Mega Bot Six Majin (Viewtiful Joe) and Giga Mega Bot Six x Six Majin (VJ 2)
What can i say? They did the TTGL thing before there was even a TTGL. Original Six Majin becomes cockpit for Mega Mega Bot Six Majin then that transforms to become the head of Giga Mega Bot Six x Six Majin. And if the design of the Giga is anything to go by its going to become the head of something in Viewtiful Joe 3, that is if Capcom ever gets around to making it.
-Megas (Megas XLR)
Even at the youngish age of 10 i had an appreciation for the Rule of Cool, despite not bieng Japanese in origin it gave the same Rule of Cool effect i would later have with the Six Majins and Guren-Lagaan.
-Metal Gear REX (Metal Gear Solid)
Less for Rule of Cool and more for the simple concept of something that could bypass the Geneva Convention concerning nuclear weapons all in a world where the science fiction hardness is rated at 7 (out of 8 which is real life).
-Guren-Lagaan and variants in order of increasing size. (We all know where from

)
An almost divine work of sheer just-in-timing and fueled on sheer willpower. Awesome in anything it does.
I would post pictures but my HTML coding isnt even worth digital cowpats.