Hope I don't mention any ones that've already been mentioned, but I highly reccomend the following....
Ali/Frazier I and III
Marquez/Vazquez I, II, and III
Hearns/Leonard I
De La Hoya/Quartey and De La Hoya/Vargas
Corrales/Castillo I
Tyson/Douglas
Marquez/Diaz and Marquez/Pacquiao I and II
Barrera/McKinney and Barrera/Morales I and III
Chavez/Taylor I
Cotto/Margarito
Forrest/Mosley I
Hopkins/Trinidad and Hopkins/Pavlik
All 3 Bowe/Holyfield fights
Marciano/Walcott I
Griffith/Archer I and II
Ali/Liston I
Trinidad/Mayorga
There's a ton more but the more I think about making a list of great fights the more I realize I'm leaving out.
James Toney-Mike McCallum 1
Simon Brown-Tyrone Trice 1
Aaron Davis-Mark Breland
Alex Arthur-Michael Gomez
Floyd Mayweather-Jesus Chavez (2001)
Marvin Hagler-John Mugabi
Pernell Whitaker-Roger Mayweather
Matthew Saad Muhammad-Marvin Johnson 1-2
Michael Spinks-Yaqui Lopez
Matthew Saad Muhammad-Yaqui Lopez 2
Frankie Liles-Tim Littles 2
Vincent Pettway-Simon Brown
Oscar De La Hoya-Fernando Vargas
Felix Trinidad-Fernando Vargas
David Tua-David Izon
Sergei Liakhovich-Lamon Brewster
Arturo Gatti-Ivan Robinson 1
Fernando Vargas-Ike Quartey
Marco Antonio Barrera-Kennedy McKinney