What is the best way to send out formatted HTML emails from Gmail?
I had a friend to use MailChimp.
She said it was easy to use and free.
Some good reading: http://www.reachcustomersonline.com/2009/01/23/09.27.00/
Remember that a lot of email clients strip CSS, add funny declarations, implement user styles, and break everything in general. Your best bet is to style it like a normal web page, and add a large "Having trouble viewing this email?
View it online" where
View it online is a link to the online version.
Gmail will send out HTML-formatted e-mail with a text/plain alternative included for older clients (or people with plain text preference) that know how to handle that sort of thing. Making a highly-customized HTML e-mail in Gmail is harder, but you can enable "Inserting images" on the Gmail Labs page to get a little closer to your goal.
Mailchimp is full featured but for a basic email Pablo's solution with Gmail is working fine. Just make sure "rich formatting" is enabled when you compose the mail