if you're looking to control from another computer you could try this:
http://forum.xbmc.org/showthread.php?tid=77985
or use the web interface. Here's the wiki page
http://wiki.xbmc.org/?title=The_Web_Interface
doesn't look like this wiki page has been updated in quite a long time, but I think that the way of accessing the web interface is still the same.
I used to like using this one:
http://forum.xbmc.org/showthread.php?tid=51596
but I've not tried it for ages, and it might not work with Dharma, which would be a shame because it was a nice, clear, and uncomplicated way to build a playlist remotely.
If you wanted to control from an Android phone you could use the Android XBMC remote
http://forum.xbmc.org/showthread.php?tid=70242
If you were wanting to control from an iPhone then you could use the paid-for app from Collect3 (though I don't think you can use this one for building playlists)
http://forum.xbmc.org/showthread.php?tid=53824
or the "coming soon" web interface for iPhone
http://forum.xbmc.org/showthread.php?tid=78508
If you're using an iPad, you could try Ultimote:
http://forum.xbmc.org/showthread.php?tid=77792
If you're using Windows Mobile:
http://forum.xbmc.org/showthread.php?tid=68330
Or for a remote control web app for generic hand-held devices e.g. PDA, or any smartphone
http://forum.xbmc.org/showthread.php?tid=40958
I can't comment on how functional or how good most of these are. I only really use at the moment is the Collect3 iPhone remote, which isn't great to be honest - it's hardly ever updated, and the lack of a playlist building function is quite annoying.
The place to read up on what remote control software / interface to use is the Supplemental tools forum. Most of the links above point to threads in that forum. So there's a starting point, now I guess it's down to you to decide what fits your needs best and find out how good each one is
