I love Moz’s interface and how they give you data on the keywords. It’s easy-to-read, making it an ideal solution for both experts and newbies alike. They’ll show you both numeric and visual representations of a keyword’s monthly search volume, its opportunity for ranking, priority, and difficulty. They’ll also show you keyword suggestions and SERP analysis, which is fantastic and detailed.
1) SEMrush - I believe that among all the 3rd party software, SEMrush has the largest keyword database. Their search volume data is pretty accurate and aligns with the Google keyword planner. Also, based on the type of content that needs to be produced (i.e. informational, transactional, etc.), one can utilize different filtering options available in it.
The team at E2M is taking this opportunity to analyze other significant (and free to use/try) keyword research tools out there. We are asking ourselves what data and logic should ideally go into keyword research, how this logic can be programmatically applied to the creation of tools, and what the best ways are to consolidate and use their output. Here’s a quick look at 25 other keyword research tools, some well-known and some you’d do well to know. These are not alternatives to the AdWords Keyword Tool on their own, but each of them performs some function of the AdWords tool in its own unique way, and all of them aid and abet your keyword research quite well.

The cost is only a one time payment…no monthly fees, which is fantastic if you’re on a budget, and you get lifetime updates and some truly excellent training videos as well as some very useful built-in tools. I’ve also tried other paid keyword tools such as Market Samurai, Wordtracker, Jaaxy, and others, and let me tell you this….none of them come close to Keyword Researcher Pro for value and ease of use.

Long Tail Pro is a keyword research tool that helps you quickly find low competition keywords for your website.  In particular, the tool is built for people doing SEO (search engine optimization) as opposed to people doing paid ads (Google Adwords PPC).  I'm sure there are some advertisers that use the tool for paid ad keyword research, but the tool was built for SEO keyword research.