System.IO.Path

GetFileName

string filename = @"C:\test\myfile.txt";
string path = @"c:\text\";
string result;

result = System.IO.Path.GetFileName(filename); 
Console.WriteLine("GetFileName ('{0}') returns '{1}'", _ 
                                  filename, result); 

result = System.IO.Path.GetFileName(path); 
Console.WriteLine("GetFileName ('{0}') returns '{1}'", _ 
                                  path, result);