LINQ

LINQ is an interesting project from Microsoft - it provides a single API for accessing different kind of data sources like databases, XML and even simple string arrays.
Here is a simple example taken from http://msdn2.microsoft.com/en-us/library/aa479865.aspx

using System;
using System.Query;
using System.Collections.Generic;

class app {
  static void Main() {
    string[] names = { "Burke", "Connor", "Frank",
                       "Everett", "Albert", 
                       "George", "Harris", 
                       "David" };

    IEnumerable expr = from s in names
                               where s.Length == 5
                               orderby s
                               select s.ToUpper();

    foreach (string item in expr)
      Console.WriteLine(item);
  }
}

Many more examples are available here: http://msdn2.microsoft.com/en-us/vcsharp/aa336746.aspx