Scott Hemmeter did an excellent write up on Kieden on Perspectives on Salesforce.

We've written about Kieden before, but it bears mentioning again because this is really a fabulous application. It allows Salesforce Marketing users manage their Google Adword buys from within Salesforce, tracking them from campaign conception through to closed business. It's very easy to set up a Google Adwords buy and using dashboards in Salesforce you can give your executive team visibility into the impact you're making.

Kieden is free for monthly spends of less than $100 so there's no risk to test it out. Other affordable pricing plans are presented on their website.