Tool: Google Keyword Tool
Link:
https://adwords.google.com/select/KeywordToolExternal
Purpose: You enter in a few keywords you think that are related to you niche, then it displays other keywords that are related that you may have not though about otherwise. It also shows competition and search volume for each keyword/keyphrase.
Tool: Webmaster/SEO Forum's
Link:
Webmaster Forum - Internet Marketing & Search Engine Forums Search Engine Optimization, Google Optimization - SEO Chat
Purpose: While I don't really consider those two places tools, I consider them a PRICELESS resource with tons of information on SEO, marketing, and other things that can be beneficial to know if you plan to be successful.
Tool: Google Webmaster Tool
Link:
https://www.google.com/accounts/Serv...overview&hl=en
Purpose: It helps you analyze your site. If your site gets penalized for any reason, or theres an error on your site that makes it difficult for the search engine spiders to index your site, 99 times out of 100 they will tell you what it is. It also helps you stay on track with the biggest keywords your ranking for, managing sitelinks, and managing your sitemap.
Tool: Google Analytics
Link:
Google Analytics
Purpose: The most comprehensive traffic tool on the net, absolutely free. It records traffic from all nations, IP's, Countries, Continents, Browsers, Screen Resolution, and even web browsers! It also tells you what keywords your site is being found for and how much traffic your getting from it.