Redundant power supply for  Catalyst 2960XR  only    
PWR-C2-250WAC=    250W AC Config 2 Power Supply Spare    $2,860
PWR-C2-640WAC=    640W AC Config 2 Power Supply Spare    $6,240
Stacking module for C2960X and C2960XR (FlexStack Plus for stacking of up to 8 switches with 80 Gbps of stack throughput)
C2960X-STACK=    Catalyst 2960-X FlexStack Plus Stacking Module optional    $6,214
(come with  0.5M stack cable already)    
Extra stacking cable for 2960S series    
CAB-STK-E-1M=    Cisco Bladeswitch 1M stack cable    $1,040
CAB-STK-E-3M=    Cisco Bladeswitch 3M stack cable    $1,560
CAB-STK-E-0.5M=    Cisco Bladeswitch 0.5M stack cable (spare)    $520
Stacking compatibility    C2960-XR IP Lite only can stack with C2960-XR IP Lite    
C2960-X LAN Base can stacking with C2960-X LAN Base  and C2960-S/SF LAN Base
Stack limit    2960-XR IP Lite stack with 2960-XR IP Lite, stack limit is 8    
2960-XLAN Base stack with 2960-XLAN Base, stack limit is 8    
2960-X LAN Base mixed with 2960-S/SF LAN Base, , stack limit is 4