After reading Ben Galbraith's post titled "Give Me My Commodity Text Widget Features, Please", I decided to create my own auto-complete text widget for Java.
I'm glad to say that I'm now using v0.1 of this tool, and it's pretty cool. I have it doing two things. First, it begins by using a standard dictionary (ripped from the Jazzy spell-checker project), so as I start typing it continually matches dictionary words. Then, as I've typed for a little while, it begins suggesting words that I've used previously, and suggests those before suggesting words from the dictionary, in essence getting smarter about what I want as it goes along.
I'll try to get this out here as a WebStart app soon. At this point I've just implemented it as a JTextPane in a JFrame, but hopefully I'll be able to do something smarter with it soon.