do this without using an "if" | if(s == "value1"){...} else if(s == "value2") { ...}

Here's one way... :)

delegate void DoStuff();

...

IDictionary<string, DoStuff> dict = new Dictionary<string, DoStuff>();
dict["foo"] = delegate { Console.WriteLine("some logic here"); };
dict["bar"] = delegate { Console.WriteLine("something else here"); };
dict["raboof"] = delegate { Console.WriteLine("of course I need more than just Writeln"); };
dict["foo"]();

Make an associative data structure. Map<String, String> in Java, IDictionary<string, string> in C#. Initialize it at the beginning of time, and then ...

Make use of the strategy pattern.

In Java terms:

public interface Strategy {
    void execute();
}

public class SomeStrategy implements Strategy {
    public void execute() {
        System.out.println("Some logic.");
    }
}

which you use as follows:

Map<String, Strategy> strategies = new HashMap<String, Strategy>();
strategies.put("strategyName1", new SomeStrategy1());
strategies.put("strategyName2", new SomeStrategy2());
strategies.put("strategyName3", new SomeStrategy3());

// ...

strategies.get(s).execute();