If you are using PHP there is a great solution for fulltext search in No-SQL database MongoDB named as MongoLantern. http://sourceforge.net/projects/mongolantern/
Previously I was using Sphinx+MongoDB to perform fulltext search, the performance was great but result quality was very poor. With MongoLantern my current search improved a lot.
MongoLantern is also listed in MongoDB site.
Please let me know if you try it of your own.
