Dear Stefani,
Google Keyword Tool, Overture Keyword Tool and wordtracker are great tools and almost everybody uses them.
But a really adwords professional would go deeper to cut back the CPC rates by searching for more specific and deeper keywords. 3 words phrases and 4 words phrases are good and take lot of time. But you need to go after 3,4,5 words keyword phrases. You can use below resources for that
1.
www.Lexfn.com
2.
www.thesaurus.com
3.
www.keyworddiscovery.com
4. spelling mistake
5. sentences
6. supplement words
7. Transposed phrases.
Obviously all above in addition to below.
1. Google
2. Overture
3. Wordtracker
Remember it is ROI what matters most not CTR. CTR matter for Google and Overture, but for you it is ROI.
Arvind Kumar