I'm a fan of Google's online calendar (GCal), but you need to do some work to get it to be synchronised with OS X's built-in iCal application. But it's worth doing, as you can then use the local application without having to have GCal open all the...
Apple Macs do have the advantage over PCs that they come with most software that you need pre-installed. However, I'm not most people, and I tend to do rather more with it. Here's my current list of what I've added to it, in rough priority order ....