Well, SpUtNiK made this rather large, rather interesting BallBlast map, with lots of corridors, and this nice big open area. When I actually get around to reviewing BallBlast arenas I will go into more detail, but for some reason, there do seem to be a lot of balls around, not just one of each, which seems like a good idea. Look at the screenshot, there are more than seven balls visible - and more arriving!
Temporarily, this is on the Custer idrive, and of course SLAM will have it on his new site. You do need the Crypt2 and Quake3a texture files to run it, SpUtNiK tells me. You probably already have them - if not, well, they are rather large, so you would probably have to be a bit of a map completist to search them out specially...