Keyword Feast will generate near unlimited amounts of new keywords for you to tune your SEO efforts around. You'll have more long tails than you'll know what to do with, and a much greater understanding of what your website visitors are actually searching for. It will also alert you of any new trends that people are searching for in your niche by comparing different sets of suggestion results from Google.
Keyword Feast workds by taking your seed list of keywords and pulling all the suggested autocompletion results from the Google suggest feature. You know the one where you type in "funny videos of a" and you'll get a list like the below appear.
Sometimes when you're breaking into a niche its best to go for the long tail search queries and this tool can generate thousands of them for you. Also if you're already in the SERPs for a good keyword but you want more traffic then sprinkle some of these long tails into your content and watch your traffic shoot up! Also the trend alert feature will allow you to find brand new keywords that have JUST entered your niche, where there is literally no competition for yet :-)
If you're planning on bringing back over 5000 keywords please bump up the delay between calls to Google to 1000 in the settings, so they don't block your IP address for making to many API queries to quickly.