Those familiar with my training style know that I am a big supporter of interval training for conditioning and fat loss.
Many of my conditioning workouts include a timing element, where you perform a certain exercise for a specified time period. For example, this article includes a Tabata interval example using the sledgehammer.
For those looking for a personal timer, you may be interested in the GYMBOSS timer. The GYMBOSS is ideal for Tabata interval timing (as well as any other interval duration).
If you are interested in timing rounds (ex. 2 or 3 minutes), you may find the Everlast timer useful.
If you workout by your computer and prefer an online option, check out this link.
Another option is to create a CD that plays music for specific time periods (ex. 2, 3, or 5 minute rounds). Ringside sells CD’s that are set to 2 or 3 minute rounds.
If budget is not an issue, you may prefer a higher end model such as this timer.
As you can see, there are several options for interval timing.