It's not for every business type, but a marketing funnel is an excellent way to get targeted customers.
There are various forms of funnels, but my favorite is in giving away a newsletter or some other incentive, like a discount or even a freebie in exchange for someone's contact information, such as an email.
The email is used to drive traffic to these existing customers as well as build a good relationship with the list of subscribers.
In using a marketing funnel you are only going to get a small percentage of these people to take any action, but that's just part of the sales funnel. You may only get 1-5% response, but with enough volume you should do exceptionally well.
If you notice many of the big name brands, they all have email marketing as part of their sales/marketing funnel... it' is because it is proven to work!