1. Take one of your non-used domains, doesn't matter what it is. Or buy a new one.
2. Put a wordpress blog theme on the domain.
3. Go to SEO Link Vine, articleranks.com, free traffic system or articlemarketingautomation.com and sign your blog up to have content delivered to it.
4.Pick categories you are interested in.
5.Set the number of articles per day to the max, which is 5 on SEO LinkVine.
6. Check your blog every day for the new articles.
7. Look at the anchor text. Viola! Keyword ideas.
Five articles per day, two keywords each article, 365 days per year = 3,650 keywords per year or 304 new keyword ideas per month.
Another side effect of this, is my PR N/A site that I was doing nothing with is a PR2 with only 115 backlinks. Now I have some ideas for the site too.