• Yahoo! Local – If you have a Yahoo ID simply enter a location and the name of a business and click Write a Review
• Google Maps – If you have a Google Account simply enter the name of a business and where they are and click Write a Review
• MyLocalLookup – Simply search for any business and click Rate It. You don’t even need an account. Businesses can get a free MyLocalLookup listing.
• Yelp is a community oriented around specific locations. It is a great way to find out which businesses others in your geographic area prefer. Sign up for a Yelp account to read and leave reviews of local businesses and receive discounts and coupons. Businesses should strongly consider getting a Free Yelp business account and reviewing other businesses they use.
• Merchant Circle is another geo-targeted community where neighbors share their opinions of the businesses they use, see special offers, discounts and coupons. Businesses can get a free MerchantCircle listing and consumers can save time and money using the new MerchantCircle Neighbors and Q&A programs.

growmap.com, MEME: BizLuv in Support of Small Businesses, Feb 2010

You should read the whole article.