Here are a bunch of command-line options. Shamelessly stolen from here.
Self explanitory. As far as I can tell, removing this flag is not enough to start the game in fullscreen. You have to restart the game with the -f flag.
Presumably, this is also permanent until you give the -w flag.
where [mode] is Software, directX, or OpenGL
where [W] is the width, [H] is the height, and [D] is the colour depth. [D] should be 16 or 32. If you aren't using the custom resolution argument, [W]x[H] has to be 800x600, 1024x768, or 1280x1024.
Put this before the -r flag if you want the resolution to be whatever you want.
[mode] can be off (for sure) or on (I think). If removing this flag doesn't give you sound back, try using it with the on mode.
Same as above, but only for music.
Same as above, but for the opening videos (EA and Maxis logos + intro movie).
Pauses the game when you switch applications (Seems like the default behaviour to me, haven't tested it myself).
CPU core count
where [n] is a positive integer. Because SimCity 4 isn't great with multiple cores, it has a habit of crashing to the desktop when this number isn't 1. By the way, the default is not 1 unless you are using a single-core machine.
I've never used this option, but apparently you can change SC4's CPU priority. I assume [priority] can be low, normal, or high. I recommend not using this option.
Brown box removal
If [mode] is off (default), SC4 will show a big brown box for missing models. If [mode] is on, it shows nothing at all.
[mode] can be off or on (default). I think this preloads all models in the background when [mode] is on.
[language] can be any of a bunch of options. Only works if you have the language sets. I belive they are found in SC4's installation directory (default C:\Program Files\Maxi\SimCity4\). In there, there should be a folder for each language. Apparently, this also affects the driving side. More info here.
Yes, you can have multiple instances of SimCity 4 running at the same time.
[mode] can be disabled, bw, color16, color256, or fullcolor.
[mode] can be disabled or enabled (default). If custom cursors are disabled, then SC4 will use Windows' cursors instead of the stylized ones.
[mode] can be off or on (default). I've heard this makes SC4 more stable, but I've never needed it. If SimCity 4 is well written, then exception handling does things like prevent your save files from getting corrupted if SC4 crashes
Input Method Editing
[mode] can be disabled or enabled (default). Apparently, this is for Asian systems. Presumably something to do with those gigantic east-Asian alphabets.
-RenderProp:,[value] -RenderProp:" [value]"
I have absolutely no idea what this does.
This is an internal command line used to indicate that a prior instance of the app launched the current instance while it was shutting down. This causes the current instance to wait for the previous instance to fully exit before proceeding. This is useful for automatic app restarting during certain operations.
Specifies the directory where the users game directory is. If the default subdirectories of "Regions\", "Plugins\", and "HTTPCache\" arn't found, then it creates an instance of, (in the case of Regions, it copies the default set over). The default game data directory defaults to being the same directory as the game installation directory. Quotes are necessary if the path name has spaces. Make sure there is a "\" on the end of your path or it creates directories like "testPlugins\" and "testRegions\"
[mode] can be off or on (default). If On, this causes the app to write a log file that describes the user's system configuration. The file is named "[computer]-config-log.txt" and is placed in the same directory as the program executable, where [computer] is your computer's name.
[mode] can be off, or the name of a server. The default is studiotech.max.ad.ea.com. Apparently, this is where the log created by -WriteLog will be sent.
Sets the code page portion of the locale for the C runtime library. Normally, the code page is determined by the language the application runs in (see the -l command line option).