I'm not a C#/.Net programmer, but LINQ is too cool. You can basically use SQL-like querying on just about any collection, whether it be an array in memory, a database, and XML structure. This is one of those "why didn't anyone think of this before?" things. Yes, there have been similar tools for querying objects for a long time, but nothing this elegant. Watch the video for a quick (well, 30 minute) intro, or, if you prefer text, read the overview document.