Here's a collection of rundll and rundll32 command lines I've collected: 

To bring up the "Format - 3 1/2  Floppy (A:)" window: 
rundll32.exe shell32.dll,SHFormatDrive 

To bring up the Control Panel "Date/Time Properties" window: 
rundll32.exe shell32.dll,Control_RunDLL timedate.cpl 

To bring up the Control Panel "Display Properties" window: 
rundll32.exe shell32.dll,Control_RunDLL desk.cpl 

To bring up the Control Panel "Display Properties" window and open the third tab (the third tab is 2 because the first tab is 0): 
rundll32.exe shell32.dll,Control_RunDLL timedate.cpl,@0,2 

To bring up the Control Panel "Network" window: 
rundll32.exe shell32.dll,Control_RunDLL netcpl.cpl 

To bring up the Control Panel "System Properties" window: 
rundll32.exe shell32.dll,Control_RunDLL sysdm.cpl 

To shut windows down using the Windows 3.1 API: 
rundll user,exitwindows 
or you can use the number that Quick View displays alongside the function name: 
rundll user,#7 

To try for a reboot using the Windows 3.1 API: 
rundll user,exitwindowsexec 
or 
rundll user,#246 

To shut Windows down using the Win32 API 
rundll32 user.exe,#7 

Make a beep 
rundll user,messagebeep 
rundll32 user.exe,messagebeep 
rundll32 user.exe,#104 

Shuts off COM2 serial port if the port was opened under the Windows 3.1 API 
rundll user,closecomm 
rundll32 user.exe,closecomm 
rundll32 user.exe,#207 

Polite windows restart 
rundll user,exitwindowsexec 

Polite power off 
rundll user,exitwindows 
rundll32 user.exe,exitwindows 
rundll32 user.exe,#7 

Forced immediate logoff 
rundll32 user32.dll,ExitWindowsEx 

Open DUN (dial up networking exported file): 
rundll32.exe rnaui.dll,RnaRunImport 

Start a dialup connection by name 
rundll32.exe rnaui.dll,RnaDial %1 

NetMeeting Speeddial CNF: 
rundll32.exe msconf.dll,OpenConfLink %l 

H.323 -or- Intel IPhone Internet telephony: 
rundll32.exe msconf.dll,NewMediaPhone %l 

URL Callto: 
rundll32.exe msconf.dll,CallToProtocolHandler %l 

URL: 
rundll32.exe shdocvw.dll,OpenURL %l 

URL Rlogin / Telnet / TN3270: 
rundll32.exe url.dll,TelnetProtocolHandler %l 

Email rfc822 EML: 
rundll32.exe c:\windows\SYSTEM\mailnews.dll,EMLFileHandler 

News rfc822 NWS: 
rundll32.exe c:\windows\SYSTEM\mailnews.dll,News_RunDLL 

URL File: 
rundll32.exe url.dll,FileProtocolHandler %l 

URL Mailto: 
rundll32.exe c:\windows\SYSTEM\mailnews.dll,Mail_RunDLL 

INF install: 
C:\WINDOWS\rundll.exe setupx.dll,InstallHinfSection DefaultInstall 132 

INF active install 
rundll32.exe advpack.dll,LaunchINFSection %1, DefaultInstall 

New briefcase 
C:\WINDOWS\rundll32.exe syncui.dll,Briefcase_Create %1!d! %2 

New LNK 
RunDLL32 AppWiz.Cpl,NewLinkHere %1 

open aif 
rundll32 amovie.ocx,RunDll %1 

play aif 
rundll32 amovie.ocx,RunDll /play /close %1 

open auf 
C:\WINDOWS\rundll32.exe C:\WINDOWS\SYSTEM\amovie.ocx,RunDll /open %1 

play auf 
C:\WINDOWS\rundll32.exe C:\WINDOWS\SYSTEM\amovie.ocx,RunDll /play /close %1 

open avi 
C:\WINDOWS\rundll32.exe C:\WINDOWS\SYSTEM\amovie.ocx,RunDll /open %1 

play avi 
C:\WINDOWS\rundll32.exe C:\WINDOWS\SYSTEM\amovie.ocx,RunDll /play /close %1 

open channel file 
rundll32 cdfview.dll,OpenChannel %L 

subscribe to channel 
rundll32 cdfview.dll,Subscribe %L 

print HTML 
rundll32.exe C:\WINDOWS\SYSTEM\MSHTML.DLL,PrintHTML "%1" 

printto HTML 
rundll32.exe C:\WINDOWS\SYSTEM\MSHTML.DLL,PrintHTML "%1" "%2" "%3" "%4" 

open midi 
C:\WINDOWS\rundll32.exe C:\WINDOWS\SYSTEM\amovie.ocx,RunDll /open %1 

play midi 
C:\WINDOWS\rundll32.exe C:\WINDOWS\SYSTEM\amovie.ocx,RunDll /play /close %1 

open MOV 
rundll32 amovie.ocx,RunDll %1 

play MOV 
rundll32 amovie.ocx,RunDll /play /close %1 

open MPEG 
C:\WINDOWS\rundll32.exe C:\WINDOWS\SYSTEM\amovie.ocx,RunDll /open %1 

play MPEG 
C:\WINDOWS\rundll32.exe C:\WINDOWS\SYSTEM\amovie.ocx,RunDll /play /close %1 

open sound 
C:\WINDOWS\rundll32.exe C:\WINDOWS\SYSTEM\amovie.ocx,RunDll /open %1 

play sound 
C:\WINDOWS\rundll32.exe C:\WINDOWS\SYSTEM\amovie.ocx,RunDll /play /close %1 

open unknown file 
C:\WINDOWS\rundll32.exe shell32.dll,OpenAs_RunDLL %1 

install screensaver 
C:\WINDOWS\rundll32.exe desk.cpl,InstallScreenSaver %l