There are tons of tools, it depends on what exactly you're trying to accomplish? Are you wanting to do keyword research, competitor research, etc? SEMRush (in my signature is a great tool) It provides you with detailed keyword information and search data for your competitors and/or your own site. This is good information to have when structuring your site. Like I said, it all depends on what you're trying to accomplish - then I can tell you what tools you need to accomplish that task.
In addition to knowing what you want to accomplish, as QuickFreeHost said, it would also be helpful to know if you are looking for free tools or are willing to invest in paid tools.
check out SEO Booster Pro, following are some of the features of it; a)Tracking: easily enables you to track your progress on search engines and find out areas you need to improve upon. b)Keywords: finds out the new keywords for you that you can be optimized for to get even more traffic. C)SEO Mapping: Assisting you on how your keywords and landing pages are related and how you can map out the right keyword-page pairs. d)Data: Enables you to download your data in CSV format and analyze it more effectively. e)Trends: based on your traffic and the pages that people have seen on your website, you can find new blog ideas to work o
Why pay $100 for it? You can get a free SEOPressor equivalent plugin for your wordpress blog from bloggerhigh.com Along with a loads of other free wordpress plugins, including one that builds 1-way backlinks for you, completely free.
I use Boostability and SEO SpyGlass (you can download the free version but i recommend you a paied version because you can save the project) These are the tools I use
What I do at this time is only limited to search for keywords to use seo tools. However, for optimization and so I still manual, because I wanted to apply here is to learn from difficulties
I personally prefer Open Site Explorer from SEOmoz for finding back links you can use for your SEO Campaign.