I have been scouring the Internet for some time now for a decent, extensible and customisable Rich Text Editor (RTE) that generates sound standard XHTML output. Having tried, what feels like, pretty much every single RTE available on the Internet I was starting to prepare myself to get back to the drawing board and consider writing my own.... that was until I came across CKEditor (formerly FCKEditor).
The new version is superb and to be honest I cannot fault it. It looks great, is incredibly easy to install and even extend with your own plugins and extensions. What's more, the HTML it generates is nice and standard. It's "Paste From Word" functionality is certainly one of the best and most accurate that I have seen.
Very pleased with CKEditor and highly recommend it for both simple and advanced RTE needs!