Yeah, and since I haven't actually used any of the methods above, I have to share mine too. As usual with Photoshop, there's fourteen different ways to get the same effect. =/

I create the icon 98x98 pixels, then go to Canvas Size, change it to 100x100, and it adds a 1 pixel border in whatever background color you have chosen. For some reason, my style borders always come out fuzzy, so I started doing it with the canvas size, and it looked neater.