Browsing around the web, I discovered two iPod touch/iPhone applications that time your contractions and then logs them for you so you can see if your contractions are getting closer together. Neat!
One is called Contraction Master ($.99). If you don't have an iPhone or iPod touch you can also use the application right from the website (for free)--provided you have the time (and sanity) to do so mid-labor. There are also applications to help you track nursing and diaper changes.
The other timer is called Labor Mate ($.99).
Check 'em out!