

I'm not sure exactly what the percentage is of, but the tool could be useful for finding related keywords. Gigablast (example search for seomoz) - Reports search counts as percentages. Could have the largest database, but they probably don't use all of it.ħSearch - Actually returns several times the number of keywords that Word Tracker does. Google Trends - Doesn't include search counts, but you can compare it against other stable keywords to get an estimate. Somebody set up a site that gets the information and lets you export it to a csv. Word Tracker - Also released a free version a week or two ago that generates the top 100 terms.

Search counts seem to be about 5 to 20 times what overture reports. Keyword Discovery - Recently released a free tool that outputs the top 100 terms. So here are 5 alternative keyword databases for you to use for overture's supplementation or replacement. Instead, use a tool built for keyword research. Numbers are scaled from a sample, and similar keywords are grouped together. It's designed for Adwords and not SEO, so competition and other metrics are given only for paid search.

But however much you value the data, you have to agree that it isn't perfect. The Google keyword research tool is the 'Keyword Planner'. (Which, despite recent reports and confusion about it's demise, is going to stay online.) I've heard some people say it's great, and some people say it's garbage. Probably the most famous, and most used, keyword research tool is Overture's Keyword Selector Tool.
