Social media and crowd-funding may be getting all the hype, but frankly the most effective way to make a sale or build an audience is through mailing lists.
You can maintain a mailing list in your email account or with WordPress plugins, but there are also many companies that offer free or paid email marketing services.
Here's a list of fifteen email marketing services to try.
I am quite happy with Mailchimp, but that is just one of the possible options. I can't recommend services I haven't used myself, but I have heard nice things about Aweber, Constant Contact, and Mailerite.
Which one do you prefer? Do you know a good one that isn't on this list?