Here's another PC-based alarm clock: Naked Alarm Clock. It's just a little Flash-based clock with ringers. Things I like about it: It's easy to program. It has loud alarms, and you can turn them off by mashing the space bar. Second, although it's Web-based, it's a self-contained Flash application, so it will ring even if your Internet connection dies in the middle of the night. It's missing a snooze alarm, though.
I might actually use this as an alarm clock next time I'm in a hotel. Yeah, I could use my mobile phone, a $20 travel alarm, or the hotel's own clock, but I figure as long as I claim to be Mr. Webware, I should be living the dream.
See also: Alarmd (review).