jEdit
I've been using JEdit for a while now, and am constantly amazed at how complete it is. It's even got a plug-in to manage XSLT transformations... Not as elegant as I'd usually like, but the integration into a kick-ass editor more than makes up for it.
WIth the addition of the Project Manager plugin, it's pretty full-featured, and the somewhat sluggish Java UI is still very usable (even on a pokey TiBook 400! (one aside on the Project Manager plugin - it seems to require Java 1.4.1 to install, but if you run JEdit once under the 1.4.1 prerelease, you can install the plugin and it still works under 1.3.1...
