Funny that a lot of us are into Cacti also. I actually posted a pic of mine in my glog last year.
I have several varieties. I'm not sure what most of them are though.
My grandpa had this ball type cactus that was about 75lbs total and had completely grown over the pot it was in. He says his original would be 30 plus years old now. About maybe 8 to 10 years ago I took roughly 12 or so balls from it and planted them. He broke most of it up shortly after. They have done well, but I've never gotten them to flower, they grow 6 to 8 in stems and have these big (5") pink flowers on the stems once per year for him.
Here are mine now, plus the original they came off of and pic of it flowering...
For him, they were more ball shaped, for me, they are all elongated.
Here is the original mine came off of...
Here are the rest of my others..
I had 2 or 3 others also, but lost them a few years ago. They are in my basement right now, but go outside during the summer months.