What is a better platform/language for developing Windows/desktop based application that can run offline (sometimes)? .NET (C#, ASP) or Java or any other development tool? This application requires to store data into a database(involves some GIS) and later Synch both ways with the main server (SQL/Oracle) during off hours or when initiated by a user or event or when online? ALso the tool/IDE recommended should allow us in the future to migrate this desktop application as a Web based application to the corporate server with less pain or re-work when internet/nw access is available to all of our remote sites/users. Any input/advice is appreciated.
You could try Adobe AIR. It seems like it would serve most of your desktop needs and it should be the easiest to migrate into a web app (Flex).
If you are strictly doing Windows desktop application development, C# or VB.NET would be an excellent choice. There is a ton of documentation out there for .NET developers. Although the framework is a free download from Microsoft, any serious work is cumbersome and tedious without the IDE.
If you needed the potential to support your application on multiple operating systems besides Microsoft Windows, then I think it might be worth looking into Java.
For web solutions, in .NET you have ASP.NET, Java you have JSP and Tomcat.
C#/WPF for desktop with Silverlight, XBAP or even ASP as the online options.
Going web-based after you already developed a desktop application is a really bad idea. There is no reason the desktop application cannot use a internet connection, and be updated from a server.
You could try Delphi. It's a rapid application development tool. Very different, but very quick to use. Well suited to Oracle integration. Data sync is probably going to need to be custom, unless you're using something like Sybase SQL Anywhere.
Since you mentioned the desire to web-enable this application at some point I'd look into Silverlight. Out-of-browser capabilities were introduced in Silverlight 3. That means that the app can run directly on the desktop, and the internet connection is optional. However, when the internet connection is available it has built-in support for auto-updating itself.
And now in Silverlight 4 it's possible to run an out-of-browser Silverlight app with elevated trust. Silverlight 4 also finally introduced things like right-click support, clipboard access, full keyboard support in fullscreen mode, etc. So if you're just now starting development, I'd most definitely use version 4.
You'll have to communicate with something like a WCF service for a lot of the database operations. But going with Silverlight should allow you to build something that'll work on the desktop and the web alike without having to manage two systems.