4. Clusty

To enhance keyword research and find additional keywords, I like to use clustering engines like Clusty. Clustering engines group search results into folder topics and can help greatly expand the breadth of a campaign.
Take a look at the following example. Using Clusty.com, the phrase "Kitchen Aid blender part" gave me the following results:
Appliances
Mixers
Food processor
Immersion blender
Replacement part
Amazon
Instead of honing in on "Kitchen Aid blender parts," these results provided me with ideas I used to create the following ad groups:
Kitchen Aid appliance parts
Kitchen Aid mixer parts
Kitchen Aid processor parts
Kitchen Aid replacement parts