I've discovered the UNIX at command, which I've set up to remind me for a certain (secret) eBay auction, and the expiration of Sittig.com. Basically, the at program will run commands "at" a certain time. For example, I told at to send me an email two hours before the certain auction closes, like this:

at now + 54 hours
echo "Check this URL:\n\nhttp://www.ebay.com" | mail -s "Auction ends soon." takoyaki

Nifty!