Given you have a good idea of where to start and are fairly confident you are speaking the same language as your client, jump start research by generating related keyphrases and long tail variants with the ever so easy to use Google Autocomplete. This tool makes predictions based on what you are typing that are a reflection of Google search activity.
2) SpyFu: I suggest to have paid account on SpyFu. I just need to find my competitors who using Adwords and review them using this tool. It will show me what ads and keywords they are using. Note that my competitor who paid for that particular keyword knows exactly that it is important for his business including recent trends. Also using SEO feature you can input any URL and find our which keywords they are ranking for.
Well, if you haven’t heard the news yet, the word on the street is Google has shut down their widely popular keyword tool for public use. Now if you want access to Google sanctioned keyword data you have to sign up for an Adwords account. Of course there are a ton of theories surrounding why Google would make this decision, some are more obvious than others. But to many of us Google’s motivations seem pointless when we still have work to do! Luckly we exist in a vibrant industry where innovation is at the core of most of what we do. As such we have a slew of different tools available to replace Google’s tool.
The limit on manual keywords could be higher. I personally wish we could input 10,000 keywords at a time, instead of 200. However, I understand the costs that Long Tail Pro has to maintain each time a new manual keyword is input. Not a deal breaker, I just wish the limit was higher. (To be fair, I don't think most keyword tools have a bulk manual option at all).