uClassify is a free web service where you can easily create your own text classifiers like spam filter, language detection etc.

You can use this web service for -
1. Spam filter
2. Web page categorization
3. Language detection
4. Written text gender recognition
5. Mood
6. Sentiment

Resources : There is a Classifier4J Java library designed to do text classification. It comes with an implementation of a Bayesian classifier including a text summary facility.