The basic setup for Nexuiz is:

Forward: W
Backward: S
Left: A
Right: D

Fire: Left-click Control
Alt fire: Right-click Alternate
Crouch: Shift
Jump: Space

Laser: 1
Shotgun: 2
Machine gun: 3
GrenadeLauncher: 4
Electro: 5
Crylink: 6
NexGun: 7
Hagar: 8
RocketLauncher: 9

Although, the entire setup is COMPLETELY customizeable by the user at any moment and changes take effect immediately - no need to even restart the game or level.