1. HTTP Uptime. HTTP uptime monitoring is important because each time website is down it a) reduces website ranking by search engines b) reduces website traffic and income c) waste PPC budget
2. External HTTP response time. Response time is a measure for user experience. When website is slow it significantly reduces user satisfaction.
3. Web Traffic Statistics. It is important by itself to analyze website visitors demographics, used browsers, referrers, etc. But it can provide more insights if combined with other metrics. For example web traffic measurement together with HTTP checks may help to find load problems when site performs slow in case of increased traffic, or together with search engine monitoring it will help to understand who is referring to your site and how much the traffic depends on the position on Google and other search engines per keywords which drive traffic towards your site.
4. Search Engine Position. Internet marketers need to watch daily website position in major search engines for sometimes hundreds of keywords which relates to website content. It helps to fine-tune search engine optimization campaigns and do competitive analysis.
5. Social Media references (Buzz Monitoring). Social Media and book-marking sites are getting more importance as a way to bring more traffic and conduct online PR campaigns for building Internet brand and reputation.
Ideally you need to have all these metrics real-time at the same dashboard in order to have full picture of your website performance. Monitis provides on-demand http and web traffic monitoring; Semonics service from the same vendor provides search engine and social media monitoring, MyBuzzMonitor could also help to stay informed and also show your reputation to your website visitors via live widget you can place into your blog or web page.