Two very easy to use blogging platforms include Posterous and Tumblr.
Posterous allows users of GMAIL, Yahoo, AOL mail and Hotmail to send an email and post to their blog. Great for people who don’t want to fuss, they just want to post text, video or photos online. Here’s a Mahalo.com post that takes you through set up and features step-by-step.
Posterous allows for integrated posting to social networking sites as well.
Tumblr is very popular for blogging or microblogging, with the sharing capabilities of social media. People add photos, comments, quickly an easily. Tumblr is particularly well suited to display multimedia with different options for text, photo, quote, link, chat, audio and video.
WordPress.com, of course, is used by many, many people as well.
For a great dissection of all the pros and cons, see Chad Egeland’s post – The Great Blog CMS Showdown: WordPress vs Tumblr vs Posterous.