I am using rclock since years and found it the best among the lot. Very easily programmable, it tells when there is mail, can give all kind of messages or in my case changes wallpaper every hour:
examples in my .rclock file
11:45; * */4/* Pay Pagibig
11:00; xsetroot -solid cadetblue &
12:00; xsetroot -solid turquoise &
12:30; play ./sound/alarm.wav
12:30 * finish take a rest
17:00 * take the dog out
Thanks for the advice. I'm using rclock at the moment.
Xonclock (which I've also used) looks good as well, almost like the clock in Vista (which whatever you might think of it at least looks good IMO).