It's worth checking out this app [update - no longer available. check out this as an alternative], if only for the great icon by David Lanham of the Icon Factory. But it's also worth grabbing if you need it for what it does:

• Keeps track of which breast was last used (indicated by the white diamond)
• Stopwatch displays the duration of the current feeding
• Shows the start time of the previous feeding
• Keeps the screen on so you can always glance at the time, hands-free
• Easy to read from a distance
• Keeps time even if you leave the app

It's $0.99 in the App Store and is by Marco Arment, creator of the popular Instapaper for iOS who's wife recently had a baby.

If you'd like to hear the full story of how it was created, you can listen to the first 20 minutes or so of Build and Analyze episode 78 where Dan and Marco discuss the idea of creating an app that wasn't Instapaper to experience the other side of the App Store.