Pocket Informant is a powerful calendar and task management app that many Windows Mobile users have been using for years and happily paying $29.95 for the privilege. The app recently became available to iPhone users for $12.99...

Pocket Information 1.02 (iTunes App Store)

It syncs with Google Calendar and Toodledo (never tried this one) but does not use data from the internal iPhone Calenadr. However, syncing with Google Calendar was very simple to configure and perform.

One of the features that iPhone uses will probably appreciate is a great week view (see screenshot above) since the iPhone's calendar only provides day and month views. The default is to start this week view from the current day. So, if you look at the week view on Wednesday, you will see your calendar out to the following Tuesday. This, in my opinion, is a very natural and useful way to look at calendar events.

If you're not quite sure you are willing to spend $12.99 for Pocket Informant, you can do what I did: Try the free lite version...

Pocket Informant LITE 1.03 (iTunes App Store)

You can find detailed information about Pocket Informant on its product page...

Pocket Informant iPhone/iPod touch