[Exhibitman]

I'm guessing the Calzaghe you reference is the signed one on my site? It is a 2011 Ringside insert.

There isn't much domestically [USA] from 1951 on:

1956 Adventure
1950s-1960s Exhibit
1991 Ringside/Kayo/AWW
1996 Ringside
1985-2002 Brown's boxing

The Brown's are fun; they cover quite a few guys with no other cards, some of whom are HOFers and some of whom are popular/interesting [Mickey Rourke, Mark Gastineau, Robert Garcia, etc.]. There are some others that are probably worth mention, like 1960s Sport Pix and Fan Fotos, if you like large format.

If you go international, there is more, most significantly the Panini series from 1965-1987. Lots of coverage of top fighters there including 'rookie' cards of Duran, Leonard, Tyson, Hagler, Hearns; basically anyone who fought in the 1970s-1980s.

The vast majority of the modern stuff is so easy to find that it isn't really worth much unless you chase plastic slabs with grades [ugh! no offense]. I tend to opt for autographed cards of modern fighters. I just find it more interesting.