Space Shuttle mission STS-119 has just landed back in Florida, after delivering the latest addition to the International Space Station. I thought this would be a good time to look at how the station grew over the years.
In November 1998, this is what the ISS looked like. That's the control module Zarya (Russian for "dawn"), which was launched by Russia and was the first piece of the ISS to reach orbit. It was, indeed, fairly small: only 13 metres long from end to end (the solar panels span a bit under 25 metres). It was joined a few weeks later by module Unity, carried to orbit by Endeavour.
By 2002, the station had grown considerably. It retained basically this shape for several years, and I guess that's the shape many people think of when they think of the ISS — "lopsided", with solar panels only at one end.
And this is what it looks like now, after the recent mission; it is now 73 metres long and 104 metres wide, with the solar panels fully extended. It is still not complete, though: there are four more assembly missions in the schedule, two by NASA's space shuttles and two by Russian crafts. Assembly won't be completed until late 2011, at the earliest.
Still, with its very large (and reflective) solar panels, the ISS is already the brightest object visible in the sky (with the exception of the Sun and the Moon, of course) and can easily be seen from the ground if you know where (and when) to look; I recommend using the website Heavens Above for that. With a reasonable telescope and on a good day, you should be able to see the shape of the station in detail, but even small binoculars should allow you to see that it's a large object (and not simply a point of light).
(and for anyone interested, NASA has a much larger sequence of pictures showing the assembly of the station; they don't yet include the results of the latest mission, though)