public static bool IntersectPixels(Rectangle rectangleA, Color[] dataA, Rectangle rectangleB, Color[] dataB)
{
     // Find the bounds of the rectangle intersection
     int top = Math.Max(rectangleA.Top, rectangleB.Top);
     int bottom = Math.Min(rectangleA.Bottom, rectangleB.Bottom);
     int left = Math.Max(rectangleA.Left, rectangleB.Left);
     int right = Math.Min(rectangleA.Right, rectangleB.Right);
   
     // Check every point within the intersection bounds
     for (int y = top; y < bottom; y++)
     {
            for (int x = left; x < right; x++)
         {
             // Get the color of both pixels at this point
             Color colorA = dataA[(x - rectangleA.Left) +
                    (y - rectangleA.Top) * rectangleA.Width];
             Color colorB = dataB[(x - rectangleB.Left) +
                    (y - rectangleB.Top) * rectangleB.Width];
   
             // If both pixels are not completely transparent,
             if (colorA.A != 0 && colorB.A != 0)
             {
                 // then an intersection has been found
                 return true;
             }
         }
     }
   
     // No intersection found
     return false;
}

class Sprite {

     [...]

     public bool CollidesWith(Sprite other)
     {
         // Default behavior uses per-pixel collision detection
         return CollidesWith(other, true);
     }

     public bool CollidesWith(Sprite other, bool calcPerPixel)
     {
         // Get dimensions of texture
         int widthOther = other.Texture.Width;
         int heightOther = other.Texture.Height;
         int widthMe = Texture.Width;
         int heightMe = Texture.Height;

         if ( calcPerPixel &&                    // if we need per pixel
             (( Math.Min(widthOther, heightOther) > 100) ||  // at least avoid doing it
             ( Math.Min(widthMe, heightMe) > 100)))          // for small sizes (nobody will notice :P)
         {
             return Bounds.Intersects(other.Bounds) // If simple intersection fails, don't even bother with per-pixel
                 && PerPixelCollision(this, other);
         }

         return Bounds.Intersects(other.Bounds);
     }

     static bool PerPixelCollision(Sprite a, Sprite b)
     {
         // Get Color data of each Texture
         Color[] bitsA = new Color[a.Texture.Width * a.Texture.Height];
         a.Texture.GetData(bitsA);
         Color[] bitsB = new Color[b.Texture.Width * b.Texture.Height];
         b.Texture.GetData(bitsB);

         // Calculate the intersecting rectangle
         int x1 = Math.Max(a.Bounds.X, b.Bounds.X);
         int x2 = Math.Min(a.Bounds.X + a.Bounds.Width, b.Bounds.X + b.Bounds.Width);

         int y1 = Math.Max(a.Bounds.Y, b.Bounds.Y);
         int y2 = Math.Min(a.Bounds.Y + a.Bounds.Height, b.Bounds.Y + b.Bounds.Height);

          // For each single pixel in the intersecting rectangle
          for (int y = y1; y < y2; ++y)
          {
              for (int x = x1; x < x2; ++x)
              {
                  // Get the color from each texture
                  Color a = bitsA[(x - a.Bounds.X) + (y - a.Bounds.Y)*a.Texture.Width];
                  Color b = bitsB[(x - b.Bounds.X) + (y - b.Bounds.Y)*b.Texture.Width];

                  if (a.A != 0 && b.A != 0) // If both colors are not transparent (the alpha channel is not 0), then there is a collision
                  {
                      return true;
                  }
              }
          }
         // If no collision occurred by now, we're clear.
         return false;
     }

     private Rectangle bounds = Rectangle.Empty;
     public virtual Rectangle Bounds
     {
         get
         {
             return new Rectangle(
                 (int)Position.X - Texture.Width,
                 (int)Position.Y - Texture.Height,
                 Texture.Width,
                 Texture.Height);
         }

     }