Hi Matthew
In order to capture more email addresses I would advise that you have some sort of incentive that makes it worth signing-up for - maybe a discount or some free aspect to your service.
I would also make sure that you customize your messages to different groups where possible - for instance you would want to hit a different angle with existing customers as against potential customers.
I imagine you are already planning on doing this but I thought I would mention it - create and integrate your form from AWEBER as this will make list management so much easier and you can create auto-responders easily. For instance if a person signs-up with your form you can have it set so that an automatic email with an introductory article or an offer is sent.
Always make sure you capture the persons name in the form so that you can personalise your email campaigns.
When sending your campaign with links to your blog I would write the email so as to encourage readers to leave comments on your articles as this will be beneficial in many ways..
I would also consider encouraging customers to forward emails that are promoting your blog posts. This will increase your traffic and will help capture more email addresses in my experience.
I would also encourage you to push your blog posts via social media as well as by email, but I would try and make sure subscribers are getting extra value for being part of your email list - like I say maybe occasional promoted giveaway or discount etc.
Chamber of Commerce specific - personal email maybe saying something like it was great to meet you at the chamber of commerce. I thought I would email you as I am starting an new periodic (weekly, fortnightly, monthly?) email about current SEO and our experiences/findings/knowledge so I thought you would be interested. As well as receiving some great information you will also be entered into a free prize draw or x amount discount on work (you would have to decide which works best for you), which is only available to those on our email list.
I find http://blog.deliverability.com/ a very useful resource when it comes to email marketing - lots of interesting information that will be of great use to you.
There are so many things you can do with email marketing and it is such a powerful tool if used right! These are just a few of my thoughts on your subject which I hope will be of help and will get you thinking...