Wordtracker - Keyword Popularity Checker
Wordtracker is an invaluable tool for the serious Website Promoter. It holds statistics for millions of search phrases and how many times they are used on the major search engines. In its simplest form it works like this: You type in a phrase that you think is suited to your website and Wordtracker will return a list of related keywords that it thinks are similar - out of this list you pick the ones that are most accurate, it will then return a refined list of phrases appropriate to these initial keywords, and statistics on how many times these phrases have been used over the last 100 days.
Based on these stats you can pick the keywords that are best suited to your site, and also pick keywords based on how much competition there is likely to be - this is very useful because if you spend time optimising your site for keywords only to find the competition for them is massive (or in fact that the keywords are not even used) then you will be wasting your time.
Once you have a refined list of keywords you can export the list to a file and use the words to optimise your site or import them into Google Adwords using copy and paste.
The downside to Wordtracker is the price: £165 per year or £29 per month. However, you can sign up for a free 7 day trial and see if you find it useful - they do take your credit card details but I will vouch for them being completely above board, I have currently taken two free trials with Wordtracker (you are allowed one a year) and I havnt had any problems canceling my account when the 7 days are up and have not been charged a penny.