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.
Moz - Backed by industry-leading data and the largest community of SEOs on the planet, Moz builds tools that make inbound marketing easy.
Startup Stash - A curated directory of 400 resources & tools for startups
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!
Startup Buffer - Startup Buffer is a premium startup directory for emerging startups all around the world.
SERPWatcher - SERPWatcher is a rank tracking tool built with focus on effectivity and ease of use. Stop wasting time with conventional rank trackers.
Content Marketing Stack - A curated directory of content marketing resources