If you are new to PPC and have never created an account, below are the links to signup with the "Big 3", Google Adwords, MSN adCenter and Yahoo! Search Marketing.
Google Adwords Signup Page
MSN adCenter Signup Page
Yahoo! Search Marketing Signup Page
Google is the largest PPC provider. Creating a new account will cost you $5 but it is well worth it. You can still find inexpensive clicks on the Adwords network and you will be able to find searchers for anything you want to advertise for, no matter how small the niche is. If you are into a larger demographic, you will pay more per click, or you just won't get many clicks. Adwords offers a Starter Account and a Standard Account. If you are new to PPC, go with the Starter Account. You can switch to the Standard Account at any time.
MSN adCenter is the newest product from the Big 3. Until recently there was no support for Mac users, but if you use a Mac and want to use MSN adCenter, you will need to download the Flock browser from Flock.com. I think adCenter is still available only by invitation.
Yahoo! Search Marketing (Y!SM) was formerly known as Overture, and Overture used to sponsor the Yahoo! search results, but that is no longer the case. Y!SM, like Adwords, is an established product but doesn't nearly have the reach that Adwords does. If you are serious about PPC, you'll need a Y!SM account. Y!SM offers a Fast Track program that will get you approved quickly and help you create and manage accounts. $199 is pretty expensive unless you just have money to blow.
It has been a few years since I last signed up for an Adwords account, over a year for Y!SM, and I'm still trying to sign up for adCenter. Currently I have an invitation but keep getting errors. I'll post my experience as it happens with adCenter.
These are the Big 3 companies in PPC. As time goes on I'll reference a few others and we'll discuss them as they come up. For now, stick to the big 3 unless you can track click fraud and have a baseline for conversions per 100 visitors.
