The upcoming Shuttle mission starting on Friday evening is a big construction project on the ISS, to move and add a large solar array to the station. The ISS currently looks a little lopsided; here's an image from December 2006:
Here's an artist's rendition of the planned work; you can see the second pair of solar arrays added. They are removing the odd array on the top; one thing I couldn't tell from the press release was whether they are storing it up there and redeploying it at a later date or bringing it back; the full ISS would have eight solar panels on each side.
I picked this image up from the STS-117 Press Kit