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There are a number of firms providing keyword management systems:
Efficient Frontier (where I work)
AtlasOnePoint
Did-It
KeywordMax
PPCPro
BidBuddy (UK)
Latitude (UK)
NOTE: if you're going to be spending a significant amount on Google, realize that it's an opaque environment where the system you use needs to be able to *accurately* model how changes in your max CPC will affect impressions, clicks and conversions. Google's Traffic Estimator doesn't work (it estimates traffic based on an average of all advertisers, & not based on how your own specific campaign performs). As far as I know, there's only one keyword management system (: that can do that.
-Shorebreak