Items:
Press Shift-~ to bring up the console and type:

juggernaut - God mode
goldblum - Fly mode
wraith - No clipping mode
positions - Show your position (x,y,z)
a_moveme x,y,z - Move to the given coordinates
dir maps - List available maps
map x - Warp to map X (X=Level name)
spawn x - Create an item or creature
ode to jack - Kill all creatures on level
impulse 911 - Unlimited ammo and items

Items:
w_saber
w_assault_rifle
w_crossbow
w_laser_rifle
w_gauss_gun
w_grenade_launcher
w_rocket_launcher
w_flame_thrower
w_chain_gun
w_plasma_generator
w_ptp_cannon
i_medical_kit
i_flak_jacket
i_body_armor
i_reflectarmor
i_heatshield
i_energyarmor
i_energyshield
i_molotov
i_gas_gren
i_claymore
i_float_disk
i_rocket_net
i_gas_mask
i_laser_sight
i_disk
i_enhancers
i_shuriken
i_implosion
i_fragger
i_radshield
i_ir_goggles
i_stealth
i_grav_belt
i_force_barrier
i_override
i_flare
i_demopack
i_energyshield
i_dome_device
i_dome_crystal