The obvious one that everyone is avoiding is JEditorPane which is right in swing. It's a pig and very limited but for certain types of HTML rendering it does ok.
I have used it for simpler jobs.
As mentioned in the other links, Lobo Browser is another option. The cobra stuff in that is pretty good and handles a lot more pages than JEditorPane. I found it does all of my medium jobs but has some frustratingly unextensible parts of its design. I use it for my help systems and some non-AJAX heavy web work.
For anything like google maps, and those sorts of heavy AJAX style web applications, you are pretty much stuck with DJ Native as another poster and the other question responses mention. Since it's shelling out to a real browser underneath the covers it will handle any web site. The only down side is that you lose a certain level of control over what it's doing since you have to make calls to it through Java script and get events back through a similar mechanism.
As an example no sane person would need, I've had applications that rendered swing controls (reports, etc.) right into the web page on the fly. In JEditorPane this was confounding but possible. In Cobra it's almost easy but a few private or final methods requiring work-arounds. In DJ Native, it would be impossible without generating the image ahead of time and making it available via URL (either local or remote).
So it all depends on your needs. For free, there is no perfect solution.