As a business, you may eventually find yourself listed on all kind of business directories (for free, whether you initiated the listing or not). Whenever you can you want to take charge of these listings to make sure that the information is complete, correct, up-to-date, and consistent across listings. You can start by searching for your business name, business phone number, and/or street address, and see where you already turn up. Many of these listings will have a link somewhere ("are you the owner of this business? claim this listing.") that you can click on to claim and take charge of your business's listing on that site. This allows you to make edits.
You could also go directly to some of the larger business sites (manta.com, hotfrog.com, merchantcircle.com) to see if you are listed on them yet, and if not go ahead and submit your information. These business directory sites won't necessarily get you reservations directly (although we did once get a guest via hotfrog!), but they do provide exposure and link-love that could help your SEO.
Then the travel and review sites -- TripAdvisor.com, Yelp.com, InsiderPages.com, Yahoo travel ... Again, you will probably eventually find yourself listed on these sites whether you want to be or not, so you might as well take charge of your listing, and learn how to manage it and respond to reviews.
Now on to the map sites -- make sure that you have a Google+ page and thus get listed on Google Maps. Also look into getting your business is listed on MapQuest.com, Bing Maps, Apple Maps, etc.... I haven't totally mastered this yet, but all of these are served by a few big geographic data companies -- the same ones that provide business data to Garmin,TomTom, and the automakers, for their automobile GPS units...
Finally, social media: Facebook, Twitter, Instagram, Pinterest..... You can take this as far as you have time and inclination -- just know that these are all sites where you need to be participating in a regular and on-going way in order to get any advantage -- you can't just create a FB page and forget about it, for example.
All of the above are free*, they just take some (a lot?) time and effort. You can do it all in one big push or you can take your time and find/claim/create/update one listing per week (or whatever). Whenever I find a listing for my business, I create a bookmark for it in my browser (especially bookmark your "dashboard.")
*nothing is totally free -- once you've registered with all these sites, you will likely get e-mail from them on a regular basis.... but you can probably create filters in your e-mail program to shunt these e-mails to a dedicated folder (like maybe the trash?) rather than cluttering up your inbox.
Also all of the above assumes that you have a decent website in the first place.
