It's an old problem: how do you allow users to format text, but still keep the data standards compliant -- in particular XHTML compliant? Some browser-based rich text editors are good at this; some are not. One company, "XStandard," has just released an ActiveX-based widget that the company claims generates XHTML 1.1 compliant output. If true, that's a pretty big deal, because 1.1 is much stricter than the XHTML 1.0 spec, particularly in its emphasis on stylesheets for layout. There's some interesting accessibility features that come into play here too. This new product probably won't be bundled into your vendor's CMS package very soon, but it's still worth a look...
Read what XStandard's head techie says about XHTML 1.1