As far as I know, there was only one An-225 ever built. It was custom-made for the transport of the now-mothballed Russian Space Shuttle Buran. And it is quite unmistakable - it is the largest plane ever built, and it has 6 engines. Here's a good resource for Antonov aircraft: (LOTS of impressive pictures)
http://www.west.net/~brianl/ruslan.htm