Google Sites and Google Apps Account (Also integrates Google Sites ) both allow you to create and edit a Site's webpage HTML.

Google Sites Supports a filtered version of Google Html (Hyper Text Markup Language). 

The filter also has a HTML Tidy for fixing minor html Errors, but this Html filter disallows Javascript and Full CSS on a Google Sites page.

Google Sites Gadgets and <Object><Embed><Form><Iframe> tags can be used to support any HTML,XHTML, XML, Javascript, Full Inline CSS. 

Most of the HTML Examples Shown have a Live Html Editor (and HTML Viewer) so you can try some Html editing online in real-time.

You can also use the Live HTML Editor directly online.