Jack Porter - Epic Games, Inc. - http://www.epicgames.com/
Based on the Unreal 1 console commands document.

changevideo » Bring up the video card selection menu

conflicts » Show objects of different classes whose names conflict.

log » Runs with the log window initially visible.

noddraw » Disables DirectDraw support.

nodsound » Disables DirectSound support.

nogc » Disables garbage collection.

nohard » Disables 3d hardware support.

nok6 » Disable AMD K6-3D support.

nolog » Don't show log window.

nokni » Disables KNI (Pentium III) support

nommx » Disables MMX support.

nosound » Disables sound.

nowarn » Disables warning message boxes on the screen.

profile » When C++ is compiled with DO_SLOW_GUARD=1, generates an UnrealScript function profile using the timings in the most recently played level only.

safe » Runs Unreal in "safe mode", avoiding loading any device drivers which could crash if there are hardware/driver problems.

server » Runs as a dedicated server. See ucc server

silent » Run silently, with no log window, and no display of error messages. Critical errors just cause the engine to exit silently.

INI=inifilename » Specify the .ini file to use for configuration. Normally UnrealTournament.ini.

USER=userinifilename » Specify the .ini file to use for user-specific configuration. Normally User.ini

LOG=logfilename » Uses the specified log file instead of UnrealTournament.log. Useful when running multiple copies on the same machine.

MULTIHOME=12.34.56.78 » Sets the "home" ip address (in numerical format) which Unreal Tournament will bind to, for a machine with multiple IP addresses.

PORT=num » Sets the UDP port number for the Internet server.

READINI=inifilename » Sets the .ini file for reading only (not for writing); overrides the INI= option.