SERPStream is a 100% free SEO tool. Members can keep track of their site's Search Engine Results Page position with updates as frequent as a dozen times a day. SERPStream have a great newsletter, sends email alerts, and have a state of the art keyword rank tracking dashboard.
Serpstat - Search analytics, Rank tracking, Backlink analysis and Site Audit tool.
Moz - Backed by industry-leading data and the largest community of SEOs on the planet, Moz builds tools that make inbound marketing easy.
SEO PowerSuite - Get all SEO tools in one pack - download free edition of SEO PowerSuite and get top 10 rankings for your site on Google and other search engines!
SEMRush - All-in-one Marketing Toolkit for digital marketing professionals.
SEO Tools Centre - SEO Tools Centre provides SEO checker services for websites.
RankTrackr - A thoughtfully designed SEO rank tracker for teams that insist on accuracy, speed and simplicity.