I heard on the Mac Review Cast today that Nvu was available for the Mac (and Windows). On its website, it is billed as rivalling applications like FrontPage (but that's not saying much) and Dreamweaver.
Personally, I prefer to write my own HTML using a simple text editor. However, I've read good things about Nvu in various Linux magazines in recent years.
I've not downloaded the software myself, so I can't say whether it's a native Cocoa application or if you need to run it under X11. I'm guessing the former; since they've gone to the trouble of building a Windows version, I assume they've done the same for OS X.