Tahini is a new Java library which aims to help Swing developers make a clean separation between the layout of their UI and their application code. It replaces scary hand-written layout or code generated by layout tools. Instead, the widgets are described in a simple XML syntax, which is linked at runtime with code written in a fairly natural Java style.
There are many tools that have this same aim. All have one or more drawbacks that make them less cool than Tahini. Most fall into one of two camps: code-generators, which pollute your source code with unreadable cruft, and loaders, which require you to jump through hoops to get at the loaded widgets. Most of these tools lead to a nasty lock-in situation, where you can't switch tools without starting over from scratch. Tahini is explicitly designed to avoid these three pitfalls.
On the other hand, most other tools are more mature than Tahini, which is still missing some obviously necessary features.
One excellent alternative, which takes a very similar approach, is SwiXML, which I encourage you to check out. Not that it's perfect, or Tahini wouldn't need to exist.
This space will soon feature more information, sample code, and a screenshot or two, but in the meantime, the code and examples are available at the Tahini project page.
You can browse the API online.