My answer:
The best keyword research tool for PPC campaigns is you.
Okay, let me come to the point. I am very new user in PPC campaign (I am new because I never run any ppc campaign by myself because of short fund and I know a little bit about SEO), I am presently working in a company as Sr. SEO/SEM/PPC executive. I have direct access on their PPC campaigns and luckily they have many campaigns running. My present company is spending approximately $228/day for these campaigns. I had basic knowledge about "how to run a ppc campaign" but I am getting real experience without expending anything by watching my company campaigns. Whenever I stuck on some issues, I check solution in Google and believe me, in a short time I have learned many important factors which can be really helpful for any campaign.
There are several factors which we should concentrate. I use Adwords, Google and Google trends to find out competitive keywords.
I am going to discuss something about dynamic keyword insertion technique...
Suppose, you are selling shirt/pants online.
In the following way you can create your ads:
Buy {keyword:shirt/pant online} (Remember you are only allowed to use 25 characters in your ads headline)
Description 1: Order now from us (Limit: 35 characters)
Description 2: Shipment is free. (Limit: 35 characters)
Display URL: yourURL.com (Limit: 35 characters)
Keywords: cozy shirts, gavardin pants, Formal shirts, Short pants, etc.
So, whenever a searcher search in Google for "buy short pants"
They will see your ads like the following way:
Buy Short Pants
So His/her search is exactly same with your displaying ads... CTR % will be higher and you will get good conversion if you can set up your campaign in a good way. There are other factors available like CPC, Max CPC, quality factors, Ad rank, Ad status, etc. you can google those techniques....
Try to find out tweaks. You will be successful.