Cassus Fett, who was briefly discussed in Knights of the Old Republic, set 4,000 years before Jango Fett.
The Mandalorians are an ancient group of warriors who fought the Jedi Knights in the Clone Wars. There are stories about them in some recent Dark Horse and old Marvel Star Wars comics. Specifically Marvel Star Wars #53.
Fenn Shysa, Tobbi Dala and Boba Fett (according to Marvel comics) were the only three survivors of the 200-man Mandalorian commando squad that fought in the Clone Wars (I know, they seem kinda young). Fett went off and became a bounty hunter, but Fenn incidentally also the name of a powerful Irish folk hero) and Toby had returned to Mandalore to fight some revolution or another. Leia got involved in it, then the rest of the characters. Fenn became a semi-regular character; he first appeared in Marvel sometime between 1980 and 1983 (obviously), but continued to show up until the comic ended in 1987.
Jodo Kast is most famous for his appearance in the Twin Eniges of Destruction, a four-part comic series written by Andy Mangles that ran in the Star Wars Galaxy magazine, issues 5-8. Jodo, another bounty hunter, acquired a suit of Mandalorian armor and went around posing as Boba Fett to get bigger bouties. Whe Fett found out he set a trap for Kast on Nal Hutta, homeworld of the Hutts. (Nal Hutta translated means "Glorious Jewel").