Lisa,

What we are using for several different ventures is Mail Chimp. They have a free tier which makes it really cost effective for building an email list. They also have a widgets that you can add to a regular website or a Wordpress site with minimal effort.

Another tool we have used is Google Forms. You can quickly create a form and post it your website or social media to gain feedback (and email addresses among other things). It has a few more steps than Mail Chimp but gives you more flexibility for capturing different types of information.

I would also suggest using social media to connect with interest users or perspective clients. Connecting with them on social media isn't going to create a database of users for you, but it will give you a great idea into who some of your more engaged connections are and you can leverage them to help you spread your message.

Oh I love questions about email marketing - This is the area I specialise and love.

It's not just about what landing page software you use (althought Leadpages & Instapage are great) structuring a landing page to convert the right people to subscribers are key. You don't want everyone and anyone signing up as they will soon unsubscribe and this can effect your spam rating.

Knowing who you clients are is important to know how to market to them and speak their language to of the upmost importance so they can resonate with your message.