This has every Luigi's Mansion site you could think of and information on the sites. I haven't found any just on Luigi's Mansion, so if you know ones I can put on, e-mail me.
Nintendo At E3
Has info, lots of screenshots for Luigi's Mansion.
Official Luigi's Mansion Site
Kind of weird. It has some information and a couple of downloads.
Other Luigi's Mansion Sites
There aren't any I could find. Please tell me one. Just e-mail me at email@example.com