Just a random list that I find interesting....

HW - Joe Louis - 25 Defenses - Lineal/WBA
CW - Johnny Nelson - 14 Defenses - WBO
LHW - Dariusz Michalczewski - 23 Defenses - WBO
SMW - Joe Calzaghe & Sven Ottke - 21 Defenses - WBO & IBF, respectively
MW - Bernard Hopkins - 20 Defenses - IBF
LMW - Gianfranco Rosi - 11 Defenses - IBF
WW - Henry Armstrong - 19 Defenses - Lineal
LWW - Julio Cesar Chavez - 11 Defenses - WBC
LW - Artur Grigorian - 17 Defenses - WBO
SFW - Tod Morgan - 12 Defenses - WBA
FW - Eusebio Pedroza - 19 Defenses - WBA
SBW - Wilfredo Gomez - 17 Defenses - WBC
BW - Orlando Canizales - 16 Defenses - IBF
SFW - Khaosai Galaxy - 19 Defenses - WBA
FW - Pongsaklek Wonjongkam - 19 Defenses - WBC
LFW - Myong Woo-Yuh - 17 Defenses - WBA
MW - Ricardo Lopez - 21 Defenses - WBC 

Of active streaks, Omar Narvaez has the most current consecutive defenses, with 15 defenses of his WBO flyweight title.  The only other fighters with current double-digit streaks are Zsolt Erdei (11) and Chris John (11).