Build an Email List. You could roll your own (We have a PHP script that loops through our database of customers and friends, and we use our SliceHost account with its fixed IP address to avoid a lot of spam-blocking issues you get if you send from a shared account's IP address.
There are a bunch of bulk email sending services. Their costs can start to add up when your list gets big, though! Using an external service means that they handle all the subscription management and they usually can do split testing and analysis. These are some ideas, not recommendations…