Lucene is one of important search engines. It provides grate search performance and easy implementation.
Here are some tutorials of Lucene :
1. Create your own search engine (Traditional Chinese)
2. Discover the Lucene full-text search library
3. A Short Introduction to Lucene
4. An Introduction to Apache Lucene for Full-Text Search
If you have more interests in it. Just go to the official website: http://lucene.apache.org/core/