Mahout currently has
Collaborative Filtering
User and Item based recommenders
K-Means, Fuzzy K-Means clustering
Mean Shift clustering
Dirichlet process clustering
Latent Dirichlet Allocation
Singular value decomposition
Parallel Frequent Pattern mining
Complementary Naive Bayes classifier
Random forest decision tree based classifier
High performance java collections (previously colt collections)
A vibrant community
and many more cool stuff to come by this summer thanks to Google summer of code
This Pure-Java library reads & writes a variety of image formats, including fast parsing of image info (size, color space, icc profile, etc.) and metadata.
This library is pure Java. It's slow, consequently, but perfectly portable. It's easier to use than ImageIO/JAI/Toolkit (Sun/Java's image support), supports more formats (and supports them more correctly). It also provides easy access to metadata.
Although not yet version 1.0, sanselan is working and is used by a number of projects in production.