I’ve put together a lengthy tutorial article on programming the iPhone (and iPad and iPod Touch) with C#, Mono and MonoTouch.
This covers a number of areas and runs through using Interface Builder, outlets and actions, table views, navigation controllers, database access with SQLite, web browsing with the WebView, GPS support through CoreLocation and MapKit, Web Services (only SOAP in this article), splash screens, icons and more besides.
You can find the article by following this link.
The article covers the same ground as the previous white paper PDF on iPhone development using Delphi Prism, but this has been fully translated over to C# and had a few areas of confusion simplified.
Update: This article has been out of date for some while, thanks to MonoTouch having moved from v3 to v5 and Xcode having moved from v3.x to v4.x and markedly changing. I've spent some while updating this extensive tutorial and the updated version can be found here.