Here is a list of some of the internet research keywords tools I recommend. Most of these have a free version and a paid for version. i just use the free versions of these keyword suggestion tools. These tools will help you find good keywords to use on the internet for your meta keyword tags. These SEO tools are a must have to be successful, they take out all of the keyword guess work. If you buy the paid for versions a lot of them give you more accurate keyword search results, keyword competition, and also some keyword market research as well. So if you do want to get the paid for versions go for it. I just like using the free versions and they give me enough information to go off of.
Of course you probably just want the list of keyword research tools, so they are listed below, but you also may want to read: search engine keywords.
SEO Book - This is probably the search engine keywords tool I use the most. Very easy to use and provides good information, the paid for version is good as well, but I just use the free version anymore.
Word Tracker - This keyword tracker is actually what powers SEO Book I believe. They provide I think the same information, but allow you to use other sources as well as give you some more information.
Keyword Discovery - This keyword discovery tool is probably one of the more expensive ones, they do have a free version, it is pretty nice research tool, I have not used the paid for version, I'd imagine it will give you a whole lot more research information on keywords and the market. This keyword research tool is powered by Trellian which also makes and entire line of SEO tools like the SEO Toolkit that is pretty popular in helping you make your website SEO!
AdWords External Keyword Tool - This is Google AdWords keyword research tool for people that do not use AdWords, so you don't get full access to this keyword tool, but if you want a cheap paid for keyword tool, signup with AdWords account, place $10 in your account for paid advertising, and you have full access to this keyword tool.
Good Keywords - This internet keyword tool is not a website, well it is, but the keyword tool is actually a program you download to use. This is keyword research tool is free and I don't think they offer a paid for version. I remember this meta keyword tool giving the number of searches a day, i thin kit will just give you the top 10 keywords. This keyword software will only run on Windows operating system I believe, I don't remember seeing a version for Mac, Linux or any others.
Another research tool you can use is the search status toolbar, this toolbar tool will tell you the rankings of every site you visit. It will tell you their Google PageRank, Alexa Rankings, and Compete rankings. This tool is useful to see what kind of competition you are up against. See what those top website's PageRank is for the keywords you want to target. This toolbar research tool is also useful when finding backlinks as you can see what PageRank that website already has. This add-on toolbar only works in Mozilla and Firefox.