Hunting for the best XML editor for Mule ESB

Recently I've been hunting for a good XML editor to use for authoring Mule ESB configuration files.

Mule is an open source lightweight ESB that is quite simple to work with, but since configuring the flows is all xml-based it can be challenging to learn the ropes in the beginning.

After starting out with the default eclipse xml editor I noticed that it doesn't cope very well with the complex namespace structures that the configuration files require.

The solution?

After trying out a couple editors I finally found the perfect match in the oXygen XML editor (http://www.oxygenxml.com/), whose autocompletion handles Mule ESB's namespaces perfectly. It also exists as an eclipse plugin, making it a good fit together with the Mule IDE (which is eclipse-based).

The downside? It's not free... So I'll be trying it out a little more to see whether the product warrants a purchase.

So, do you have an alternative xml editor that you can tip me about, and preferably a free/open source one? Give me your thoughts, especially if you've been using it in conjuction with Mule.

Over and out...