Whilst I am somewhat biased, Word of Mouth has always been the most successful channel for gaining repeat and new business for me.
Take a look at this case study on my website -
http://www.brand88.com.au/case-studi...ious-pigs.html
Quick figures - $10k to design, produce and distribute beautiful custom ceramic piglets, with the business logo on them.
6 years later, these wee piggies are still bringing in referral business, and generating word of mouth conversations about Curious Design.
Another channel that worked really effectively for me, was creating a referral system around my champions, advocates and users of my service. No money changed hands at all, but by working this simple system for half an hour a day, we managed to bring in over $650k worth of billable consulting in 39 weeks.
Again, I'm somewhat biased, but investing your marketing dollars into your existing base of clients, will see a far greater return than yellow pages or local paper adverts.