We already know about the two otaku heavens - Akihabara and Nakano Broadway but there is another place which may become the 3rd Otaku heaven west of Tokyo in a city called Tachikawa.
The latest edition of Windows 100% had a wee article on what they called "the 3rd otaku city" and seeing that I was in the area anyway, I thought I'd check it out. Sure enough, I was greeted with a load of Gunpla when I arrived on the third floor of Daiichi Department store.