JCE is in my list of top 3 favorite extensions, and the new 2.0 version is sweet! You have so much power with this editor! It supports all important media types (direct input of youtube links, files, flash, images), has time saving features like the article template manager, and even allows you to use its built-in screenshot/popup manager.
It replaced at least 5 extensions you would otherwise need to install.
The interface is clean. It is stable, every thing is optional.