These are some I know of the top of my head.
R.I.P.

* Johnny Owen died from a blood clot he suffered from a fight with Lupe Pintor in 1980 (2 months after the fight)

* Deuk Koo Kim died from injuries 4 days after his bout with Ray Mancini in 1982 (The referee & Kims mother commited suicide 4 months later)

* Jimmy Garcia died from injuries 13 days after his bout with Gabriel Ruelas in 1995