Google recently introduced Google Sitelinks which enables the advertiser to add 4 additional links underneath the ad. You can choose any links that you feel are relevant to your searchers. Unfortunately, this is not enabled for all advertisers. According to Google:
Currently, the option to set up Ad Sitelinks will only appear for advertisers whose ads meet a certain high quality threshold. If your account qualifies to run this feature, you'll find the option to set up Ad Sitelinks in your Campaign Settings tab -- it will appear as "Show additional links to my site" under the "Ad extensions" section.
Here's how to enable it:
1. Log into your AdWords account.
2. Click the Campaign Settings tab and go to the Show additional links to my site section under Ad extensions.
3. List the names and URLs of up to 10 internal links (prioritizing the most important links first).
4. Click Save when you've finished adding your links.
5. If a search triggers your ad to run with Ad Sitelinks, this new system may include up to four of your additional links on your ad, along with the main landing page link.
For our site, this shows up only when someone in Canada types "canadian web hosting". It does not show up for any other keyword searches.