ABOUT US LINK
Have a link to your About Us section, which should include basic information about you or your company. This allows users an additional opportunity to ascertain the nature of your site. It is important to try and put a face to a company.
CONTACT US LINK
One of the biggest issues that I find when we review sites is sites that have no way to contact their owner or webmaster. It could be as simple as you wanting to let them know that they have a typo, or as beneficial as wanting to request a quote for their services. It is important to have multiple and thorough ways of being contacted. Also, if you are using a captcha on a contact form, test it yourself to see whether or not it is comprehensive or frustrating.
TERMS OF SERVICE
If you are providing a service or a product, this is your chance to link to all of the good legal jargon. This is a great self-protective measure and is very important to have. Placement of this in the footer is a very standard location and users would anticipate it being there.
If you are handling sensitive information, or capturing peoples email addresses or passwords, it is good to state how you plan on keeping that information safe and what information you may be logging when users visit your site. Again, this is a self preservation measure and it is good to have all of your ducks in a row, as well as assuring your users that they can trust you.
Linking to your site map allows users a place where they know they can locate how to navigate the rest of your site. This way, if anyone gets lost they can find their way right there in the footer. As many people who are getting lost will scroll all the way down a page, this is the perfect location for that link.
ADDRESS AND PHONE NUMBER
If you have a physical business, offer phone support, or have a reason for people to mail you things, putting that information in the footer is an anticipated and appropriate location. Be sure to give people the correct information that they need.