I use iCal on my Mac and the iOS calendars from Apple quite a bit. I would never have even thought about using a 3rd party app on my iPhone, but Easy Calendar has changed my mind.
It's the 'easy' part that I like the most. Using it reduces the taps to create events, from 6 to about 3. Events can be edited with 2 taps, and navigating to different days or weeks is also easier than the stock iPhone calendar.
The app syncs with MobileMe, Outlook, Google Calendar and other CalDAV apps. Alarms are supported, and it is multi-lingual in Spanish, German, French and Dutch.
Easy Calendar is usually US $3.99, but the price has varied a bit over the months with sales. Of course free is the best price of all, so if you want to try it, grab it today and see if it makes keeping up with events and appointments a bit easier. Here's a video if you want to see how it works.