Sure thing...
Set Volume Percent: "http://ipaddress:port/xbmcCmds/xbmcHttp?command=ExecBuiltIn¶meter=XBMC.SetVolume([0-100])"
Set Time Percent: "http://ipaddress:port/xbmcCmds/xbmcHttp?command=SeekPercentage([0-100])"
Play Controls: "http://ipaddress:port/xbmcCmds/xbmcHttp?command=ExecBuiltIn¶meter=XBMC.PlayerControl({Command})"
Commands can be {Play, Stop, Forward, Rewind, Next, Previous, BigSkipForward, BigSkipBackward, SmallSkipForward, SmallSkipBackward, Random, Repeat, RepeatOne, RepeatAll, RepeatOff, Partymode(music) or Partymode(video) or Partymode(path to .xsp file), and Record}
Key Presses: "http://ipaddress:port/xbmcCmds/xbmcHttp?command=SendKey({ButtonID})"
ButtonID's: {Up:270,Down:271,Left:272,Right:273,Enter/Return:256,Back:257,Info:261,Add/Remove from Queue:259}
There are lots more ButtonID's (see [Key.h](http://xbmc.org/trac/browser/trunk/XBMC/guilib/Key.h))
There are also Built in actions that can be accessed. (See [List of Built-In Functions](http://xbmc.org/wiki/?title=List_of_Built_In_Functions). You can call them with "http://ipaddress:port/xbmcCmds/xbmcHttp?command=ExecBuiltIn¶meter="
If you need any more help, let me know. Most of my info was taken from [XBMC HTTP API](http://xbmc.org/wiki/?title=Category:HTTP_API)
Wolfie