A useful tool for SEO when you have to glance at pages to check in on success of your promotions to see how many Visitors your pages are having at any time. But I can't promote it in this section. So you'll have to figure out what I'm referring to.
I think there is no need of any tool to perform SEO process... Its not entertained by any search engines... To obtain a effective output do it manually as possible...
I knew about some SEO tools(and use them) they can help us to maintain our websites. like seositecheckup, rank tracker, etc.
I am suggesting you some of the best tools that really make your work so easy. 1.) Google Analytics Tool- It shows the detailed statistics about the visitors to a website. 2.) Google Adwords Keyword Tool- It suggests you to select the best keyword that is most related to your product. 3.) Google Webmasters Tool- It allows webmasters to check indexing status.
I've not tried/used any third party applications/tools for SEO. I do use Google webmaster tools, Google Analytics for optimizing my website to search engines and to check the analysis of my website and some tips to improve my website's performance in the Google.
Try Google SEO services tool, these are really perfect and powerful tools, you can also try Seomoz.org for SEO blogs and Tools.