I\'m developing a little project plan and I came to a point when I need to decide what local databse system to use.
The input data is going to be stored on webserver
The "obvious" choice would be MS SQL Server Express. VS and .net both support it natively and if you've experience with it already (for the main DB), I'd certainly be tempted to stick with it (or its express version).
But that's certainly not the end of your options. I use SQLite a lot for cross-platform applications and web-apps. It's eye-wateringly-fast and it does integrate pretty well through System.Data.SQLite -- albeit not as tightly as MS SQL Server.
There's also a Compact edition of SQL Server that compares quite well to SQLite.