The keyword phrases to use for your PPC account aren't always obvious. A key to great ROI and customer loyalty is to have customers think that you're the only viable solution to their problem at a given time. Therefore, the challenge in keyword research is not coming up with keywords. That's the easy part. You just scan the website and use the product names and there you go...a keyword list.
The challenge is in exploiting markets that become successful that competitors may not have thought of. That's why it's important to always be practicing keyword discovery and exploring phrases that might work well by always testing.
This comes by developing correlations between what you're offering and phrases that searchers may be typing. This brainstorming may be one of the best investments of your time. Although search is about delivering the right solution at the precise time that a searcher is looking, there are keywords markets out there where you may be able to distract a searcher from the information they thought they wanted. After all, people don't always know what they're looking for.
If you continue to add new groups of experimental words, you will discover less expensive markets that will work for you. Once you've identified your target markets, the game becomes a strategic brainstorming exercise of imagining their online search behavior. Whatever your field, make it your goal to double your click volume, targeting extremely targeted searchers, on keywords that should be priced at rock-bottom levels (due to other advertisers being too lazy to do this). In most cases, your ROI will improve substantially.
For example, let's say you have a site that sells iphone apps. Many of your keyword choices will be obvious - "best iphone apps, cool iphone apps, must have iphone apps, etc." But, what about markets that aren't quite what people are looking for, but you may be able to turn into a profitable market for your business? How about how to unlock iphone? Take a look at your competition here -
Look at this cheap real estate! You could write an ad like "Unlock Your iphone - Then load it here with the best apps on the market." Now, I'm not saying that the majority of your business will come this way, or even that this specific keyword phrase would actually reach this advertiser's marketing goals, but the prices of your clicks here will be way lower than on any "iphone app" keywords and if you can pull a good enough CTR and conversion rate, you're in business.
The one thing I do know about your results here is that if you don't try it, it won't work.