Alexa: basic analysis of any website(s)' traffic data (detailed information is only available for websites which have a minimum ranking)
Google Analytics: free service that gives you access to the analysis of your website(s)' traffic data
Google AdWords: lets you create ads and choose keywords to enable your ad to be contextually displayed, either next to search results on search engines' sites that are part of the Google Search Network (search network advertising) and/or next to content on sites that are part of the Google Display Network (content network advertising)
Google AdSense: Google's contextual advertising solution for web publishers — delivers text-based Google AdWords ads that are relevant to site content pages
Google Webmaster Tools: Google's platform providing detailed reports about your webpages' visibility on Google (crawling, "+1" button stats, etc) — also contains links to Google Analytics, AdWords & AdSense
Woopra: real time web analytics (including tracking conversion and funnel reports) and live chat
WebmasterWorld.com: news about Social Media, SEO, online marketing, etc.
