Tools and methods for discovering new related keywords?

I have various methods for discovering more and more "long tail" keywords, but I’ve yet to figure out a good way to find more/all of the different but related groups of keywords that might work for a campaign. I’m wondering what tools people are using to help brainstorm new ideas. Just sitting down and brainstorming works well, but you always miss a ton of ideas too.
For example, say my primary keyword/theme is "making money". This is just the first example that came to mind. You could generate a huge list of long tail keywords that included "making money", but there are a bunch of other phrases you could go after such as "work at home", "extra income", "earn money", etc. Each of these could end up with 1000 long tail keywords each, which is the easy part once you have the idea, but I’m looking for a good systematic way […]

Original post by pppatrick