These two squirrels (1 black, 1 grey) were raised by a black female in summer, 2010 and have never left each other's side since then. Here's a link to the original post.
They run, scramble, wrestle, share food and seem to find great comfort in each other.
Perhaps other squirrels have best buds, but it's difficult to tell. This pair really stand out though and I look for them every day.
Meanwhile, down in the basement, there are other things to look for every day now.
Click the pic.