Italian Cycling Journal has a nice series going about Italian steel tubing manufacturers. They start with a very in depth article about Columbus tubing, which was a favorite of some of the more well known builders -- Colnago, Pinarello, Eddy Merckx & De Rosa. The next in the series is a blurb about a little known manufacturer called Falck, which is thought to have been used more than people realize but decals are rarely seen. Falck tubing was used by framebuilders like Legnano, Casati, Guerciotti, and Concorde.
After that we learn about Castello Mario & Figlio of Torino, of which not much is known. The only manufacturer that the author knows of to have used the tubing is Rabeneick, a German builder.
The most recent article is about Oria tubing, a favorite of builders like Montagner, Torelli & Cramerotti.
I'm assuming that we will see a post about Dedacciai tubing, and maybe some other crazy shit we don't know about, in the near future.