Marketing tips?

I am designing a website for my dad's plumbing company and we are also looking for other inexpensive and/or free ways to market his company. It is not a new company (he's been in business for 21 years) but he wants a way to boost customer base, both commercially and residentially. Other than free web ads and building a website, what other ways can he market his company? From a customer standpoint, what things do you like to hear when searching for a plumber or any contractor? And what things would be ideal to see on a plumber's website?