exactly google will help you but by you saying which keywords are hot some keywords are always hot so you have to figure out which ones you need
Google trends gives you all the hottest keywords like the other guy said, then just dig a little deeper. Find more keywords in the hot niche.
To be successful in getting the right keyword you should know the niche and the type business of your client. Think as if you're the owner and the visitors of the site. In this was you can come up with bright ideas in picking the right keywords for your site. Keyword Suggestion tools that you can use are: freekeywords.wordtracker.com/ keyworddiscovery.com/keywords.html tools.seobook.com/keyword-tools/seobook/
The hottest keyword on the internet is obviously: make money online but if you can dominate that niche let me know!