I'm working on lightweight CMS concepts for a (potential) new project these days, and have been looking at wysiwyg editors that work (meaning work) in a browser.

htmlArea, currently added to the Cocoon Forms samples, is still in beta for mozilla but already looks very usable. I can't wait to try it on actual content (like that cool prototype from the FlowLimitationCircumventer people ;-), as it seems to be in widespread use already.

An alternative would be to use a java-based thing like hexidec Ekit. The drag is that clients need the Java Plugin, but once it's installed the risk of running into browser incompatibilities should be lower, so it might be a good alternative to javascript-based solutions.