OOP Applications

Hi there... I''ve recently got into C# and am looking to use it to make some large scale applications which will require careful planning. I''ve used OOP very loosely before in C++ using objects etc. but never made the whole application from an object. Are there any good tutorials or sites people can recommend about using OOP to create applications, in particular Graphics Engines etc. Alternatively, some source code / application structure or something of a similar nature would be helpful. Cheers, Synex Code Monkey