I beg to differ!
BLENDER is definitely one of the very best open source packages ever!
And there is a x64 version: Blender
It does not have an installer but comes in an archive...still, it is 64-bit! =)
By the way, I was going to post about GIMP, but I tried their x64 version and was not running well on my Windows 7 RC. It started up, but the menus weren't working correctly...but maybe others will have better luck?