The Code Beside blog has a StaticStringDictionary implementation using LINQ expression trees.

Glenn Block has an implementation of ForEach for IEnumerable:

  1: public static class IEnumerableUtils {
  2:   public static void ForEach<T>(this IEnumerable<T> collection, Action<T> action) {
  3:     foreach(T item in collection) {
  4:     action(item);
  5:   }
  6: }

Eric White has a post on finding duplicates using LINQ.  Here is the sample:

  1: int[] listOfItems = new[] { 4, 2, 3, 1, 6, 4, 3 };
  2: 
  3: var duplicates = listOfItems
  4:     .GroupBy(i => i)
  5:     .Where(g => g.Count() > 1)
  6:     .Select(g => g.Key);
  7: 
  8: foreach (var d in duplicates) {
  9:     Console.WriteLine(d);
 10: }

Robert Shelton has an updated list of LINQ Providers.

Well, not really, but The Great LINQ shows a usage of LINQ to Objects over a chemistry domain:

from atom in molecule.Atoms
where atom.Element == Element.Hydrogen
and atom.Bonds.Count == 1
from atom2 in atom.Bonds[0].FindAtom(a => a != atom && a.Element == Element.Oxygen)
where atom2.FindBonds(b => b != atom.Bonds[0]).Count == 1
select atom2.FindBonds(b => b != atom.Bonds[0])[0].FindAtom(a => a != atom2)

Igor Ostrovsky has a post about 7 tricks to simplify your programs with LINQ.

#1 is pretty cool:

int[] a = Enumerable.Repeat(-1, 10).ToArray();
int[] b = Enumerable.Range(0, 10).ToArray();
int[] c = Enumerable.Range(0, 10).Select(i => 100 + 10 * i).ToArray();

I disagree with #2 - it has serious performance implications.  Go check out the link to see them all...

Derik Whittaker has a post on Using LINQ's DataContext to Recreate your Database for Testing.

In my opinion the let keyword is one of the most power features of LINQ.  Stuart Leeks posts about using let in LINQ to objects.

var query = from fileSystemInfo in fileSystemInfos
        where fileSystemInfo is FileInfo
        let fileInfo = (FileInfo)fileSystemInfo
        where fileInfo.Length < 1000
        select fileInfo;

Frans Bouma releases LINQ support for LLBLGen Pro.

Claudio Lassala shows us how to build LINQ queries step by step.