What is the best way to get the executing exe's path in .NET?

From program a.exe located in c:/dir I need to open text file c:/dir/text.txt. I don't know where a.exe could be located, but text.txt will always be in the same path. How to get the name of the currently executing assembly from within to program itself so that i can access the text file?

EDIT: what if a.exe is a Windows service? It doesn't have Application as it is not a Windows Applicaion.

Thanks in advance.

I usually access the directory that contains my application's .exe with:

System.IO.Path.GetDirectoryName(System.Reflection.Assembly.GetEntryAssembly().Location);

string exePath = Application.ExecutablePath;
string startupPath = Application.StartupPath;

EDIT - Without using application object:

string path = System.IO.Path.GetDirectoryName( 
      System.Reflection.Assembly.GetExecutingAssembly().GetName().CodeBase );

See here for more info:

http://msdn.microsoft.com/en-us/library/aa457089.aspx

Application.ExecutablePath

Application.StartupPath