I realized soon after I posted my previous entry on text mining tools that I missed a few. Here are a few more to keep you busy:
OpenNLP - hosts a variety of java-based NLP tools which perform sentence detection, tokenization, pos-tagging, chunking and parsing, named-entity detection, and coreference using the OpenNLP Maxent machine learning package.
Text-Mining.org - a portal for news and information in the text mining community.
Kernel Machines - a portal on Support Vector Machines and kernel methods. It includes articles, tutorials, news, book references, and much more. If you want to learn about SVM classification, start here.
Carrot2 - Open source search result clustering software in Java. It interoperates with Lucene and as an add-on for Nutch. They have a gone on to create a commercial text clustering software called Lingo 3G.