Look at your local advertising opportunities, and if you make a website, for goodness' sake make it a professional-looking one. As a consumer I am instantly turned off any product with a shoddily-made website.
I couldn't agree more with that statement! I have passed over barns that I saw online just because of their website. I know getting a grand old website isn't cheap, but I would suggest at least exploring your options.
Things I like to see on websites are:
Pictures of the barn
Pictures of the turnout spaces
Pictures of other amenities (indoor arena, tack room, wash stall, outdoor arena(s), round pen, etc)
Prices of board/lessons/other services offered. (I don't like wasting my time if I see a really nice place online only to find out, through talking on the phone or going there, that they are out of my price range.
Pictures of horses (whether being ridden, out in the pasture, etc) That way I can see the conditions of the horses prior to going there.
If you wanted to, maybe even have a "Boarders" page. Where there are pictures of the horses and owners. Some people might feel more welcome if they see the names and faces of people already there (it kind of takes away from the "new kid on the block" type feel.
You could even put up upcoming events on their too.