I've discussed the IBM Java Developer Kits that you can download and use, including the new J5SE betas. We now have a JDK for the Apache Harmony project.
IBM Development Package for Apache Harmony is for use with Apache Harmony, which IBM is participating in. IBM says this JDK can be used with the Harmony code but is not (yet?) part of the Harmony code (which I think explains why you have to download it from our site instead of Apache's). The JDK is free, but unsupported.
IBM Java Developer Kits: JDK for Apache Harmony