I think that for volume, the best bet is still Google. For ideas, though, SEMRush, wordtracker, and even Bing are good places to start looking. "Don't hit enter" - or suggester.promediacorp.com is also good for ideas. Then we can throw these into Google last to see if there is really any demand out there or not.
QUOTE(Boris Cain @ Sep 24 2013, 04:51 PM)
Write down the main categories of your business and the terms or phrases that might fall under each of those categories. Include terms or phrases your customers would use to describe your products or services.
You can get keyword ideas and traffic estimates to help you build a Search Network campaign by using the Keyword Planner. This tool will also show you how a list of keywords might perform and the average number of times people searched for those terms. This can help you decide which keywords can help drive traffic to your website and increase awareness of your product,
In some cases, you'll want to prevent your ad from showing for terms that aren't relevant to your product or service. Try adding negative keywords to help you reduce costs and make your ad appear only for the search terms you want.
The search terms report gives you information on what people were searching for when they saw your ad and clicked on it. This information can help you remove poorly performing keywords or add new ones. You can also use the search terms report to help you identify negative keywords.