Splash ID is another option. I use it because I'd used on my BlackBerry and already had a data file which I could import into the iPhone version, so I didn't check out the competition. The desktop-handheld sync is a little awkward, because it has to be done over wifi and initiated manually.
It's got great flexibility as you can customise all the categories and even the fields in individual records. Costs $10 from the App Store, with the desktop companion app being a free download once you've installed the app on your iPhone.