Since I published my article on using CSS in HTML emails a few days ago, there has been a couple of great articles published on the same subject. I want to highlight some of these, and some other related articles that I didn't mention in the post.

Ensuring your HTML emails look great and get delivered
David Greiner has an article up on Think Vitamin which covers some of what I covered, but goes more into detail on actually getting the emails delivered if you are sending them yourself.

Email Standards Project

The Email Standards Project is about working with email client developers and the design community to improve web standards support and accessibility in email. The project was formed out of frustration with the inconsistent rendering of HTML emails in major email clients.

They have a "State of the Clients" section which shows how the major email clients are doing as far as supporting standards.

Web Standards in Email Clients
Fed up and spreading the word.

A Guide to CSS Support in Email
Quite a comprehensive article on what clients support what. Also includes a very nice PDF Download. Also written by David. Apparently Dave is the man when it comes to this stuff =)