Here's a small script (macosxhints mirror) that reads the data files that iCal dumps to, and prints out a small, text-only version of today's events. I use it with GeekTool, and have it display the output on my desktop.
You need to edit the script a little for your own machine. See the comments at the top -- it shouldn't be too hard. You'll also need to make it executable (chmod 755 script_name) before it can be run.
[robg adds: The customization required is identifying which calendar belongs to which filename. An easy way to do this is to open the Info.plist file in a text editor (or Property List Editor) and look for the value next to Title. Once you know that, you can copy the corestorage.ics file in the Finder, switch to Terminal, and then paste it into the right section of the script to avoid typing that long path by hand. I tested this, and it works well.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060918145206393