What other frameworks are there for general data structures?

The Generic Collection Library for Java - JGL from ObjectSpace has been around since 1996 and the same version works with both JDK 1.1 and the Java 2 SDK. Doug Lea's Collections Package is a precursor to the current Collections Framework. If you are looking for template support, the Generic Java Language Extension includes a retrofitted version of the Collections Framework with template support. A new entry into the mix is Colt which is meant for scientific computing, and includes data structures for numerical operations.