I'm the type of person who does a lot of research on a certain product, restaurant, book or movie before I buy, and I believe that consumer reviews are the most valuable information, next to the actual product. Reviews allow new customers to ease into becoming more comfortable with the potential product or service they are considering investing in.
There are many websites that allow you to add a review about your business, and it's best to let your customers know about these sites so they can return the favor by writing up an honest review. For local businesses, I am a big fan of Yelp.com, which has become popular with local restaurants, but you can basically review any type of business under the blue sky.
A great way for customers to leave testimonials for your business is to direct them straight to the review website, whether it is a link in a thank you email, confirmation page, or in a prominent area on your website.
Other popular websites to view and write consumer reviews are:
Merchant Circle
CitySearch
Google Maps - easiest if you already have a Google Account
InsiderPages
Judy's Book
Kaboodle
Of course, it's best to take any review written with a grain of salt, since anyone can create reviews.