Pocket Informant is one awesome application and does exactly what you are looking for. As far as simplicity goes, adding appointments or tasks is no different than any other application. PI syncs with Google Calendar or it pulls the calendar info directly from Apple's built in calendar thus making it able to sync via MobileMe as well. In addition there are several calendar views be it weekly, monthly, daily etc.
I enter all my calendar information into Outlook 2010 and then it automatically syncs via MobileMe to the built in calendar. When I start Pocket Informant it's all there.
The task list is simple and can be configured to work with GTD or Franklin Covey methods plus it syncs seamlesly with Toodledo. If you use other Toodledo apps on the iPhone, they will all be in sync and you can use the Toodledo website to add tasks easily as well. There is also a utility that syncs toodledo with Outlook or iCal as well. The developers of Pocket Informant also created a utilty to sync with Outlook.