Hey Everyone,
I would strongly suggest Keyword Companion. I own version 1.0 and when 2.0 comes out on September 12th, it will blow every other tool right out of the water!
It's not free, but it's worth it. Just go to the site and in a few days you'll see a promotional video with what it can do:
keywordcompanion.com
It manages huge keyword lists, it forms ad groups, it pulls competitive ads and it imports them into your adwords account and yahoo and miva and enhance. AND it will incorporate the Google API and keyword research soon, so it will be all a marketer needs. And I didn't even mention the cool plug-ins...
They're giving away a free audio eBook for now, here's the link again:
keywordcompanion.com/keywords_conversion_continuity.html
Sincerely,
Ioana