Seems you are pretty ambitious...gud fr u..
1)First of all, for your first requirement, a DB driven corporate application which you wana run on multiple platforms, I am afarid one single language won't suffice.
For Windows, you may go for C# as the dev language, SQL as backend and Visual Studio 2010 as IDE.For this very app on Apple platform, you will have to learn another language, Objective C i guess.
2)For ur second requirement, you can go with C# and VS 2010..for rich UI stuffs u cn use WPF,HTML5,CSS 3.0,AJAX..even you can embedd JQuery Codes and stuffs...The dev langugae may be C# and all these above will be actually add ons to make your website look attractive n quite appealing.
3)For your 3rd requirement, a multi platform mobile application, I guess Java will do..you can code Android and Iphone apps in Java...even you can code Android in C#...Not very sure about Blackberry
4)Same applies for your mobile phone game...
But on the contrary I will suggest that you either start with one platform at a time and start to code your apps...If you start with .NET and C#, you can easily achieve your most of the objectives, except for multi platforms stuffs...Because attempting these on a single platform itself will be a hectic task..believe me..it takes a lot of time and a hell lotta efforts to code something when you are pretty new..But patience will take you there..