Search engine against IEnumerable objects

We开发者_如何学C have a .NET application on which has grown beyond what we can develop in-house to search. We can certainly try to make the best search algorithm we can be it's not what we do and someone else has certainly done it better.

We have an IEnumerable of object which has a title and a description and we'd like to search and rank it by relevance, kinda like the stackoverflow search. What's a good free library we can make use of? No SQL.

You may want to check out Lucene.NET. It's a port of Lucene, the defacto standard of free text search in Java.