This script will allow you to automatically and periodically check the U.S. Apple Store (refurbished section) for a given product. It will notify you whether that item is available or not. The script needs to be placed into /usr/local/bin and requires you to set up a crontab file (instructions are included in the script). This is based off of another script found here.
Here's my script; copy and paste the contents into a new file in the Terminal using your favorite editor and follow the instructions in the script to make it work for the product(s) you are interested in watching.
[robg adds: Due to long line lengths that aren't easily broken, I've put this script online as a separate text file which will open in a new window.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20040415115836661