Online directories and local search sites are the modern equivalent of the Yellow Pages. More targeted than paid search advertising or banner ads, a listing on one of these sites will help customers in your area find you — even if they start off looking for someone else. Google Places, Bing Places, Yahoo Local Listings and Citysearch are solid places to start.
Customer review sites like Yelp, Foursquare and Angie's List are an extension of the local listing category — you're featured in a list or a searchable map along with other area businesses, and potential customers can decide if they'd like to support your business based on the reviews they read. For businesses with lots of reviews (especially glowing ones), review sites can be a boon. But if you're freshly listed and have only three reviews, one of which isn't so glowing, your star rating will suffer. The trick here is getting as many reviews as possible so the bad ones won't drag you down. If you have plenty of reviews and a still-low rating, well, that's a different problem altogether.