TimeLeft - TimeLeft is a versatile desktop utility - it can be used as a countdown clock, reminder, clock...
Hourglass - Hourglass is the most advanced simple countdown timer for Windows.
wnr - Better than pomodoro, this timer app balances work and rest.
Free Countdown Timer - Free Countdown Timer is a free, full-featured and user-friendly countdown timer for Windows
Gestimer - For those little reminders during the day
LClock - Longhorn systray clock program