Akismet – spam comment filtering tool
Google Analytics – its free, its by Google.
Statcounter - another free analytics programme. This is my personal choice of analytic programme.
Feedburner – looks after your RSS feeds and gives you lovely nerdy stats about your feed.
Adsense - Googles very own ad network. Probably the most used.
Amazon Associates - where you can make money on the books etc you recommend
Copyscape – the place to check for content theft and plaiarism
Elegant Themes - my personal favourite if I had to choose one
WordPress.org – the one where you have to have it hosted somewhere but comes with whistles and bows. Parenting Directory is run on wordpress.org
WordPress.com - the free version but does have limitations.
Blogger - like wordpress.com this is a free hosted one and will have limitations, oh and this one is owned by Google