What is the best way to grow an email newsletter list organically with no help from marketing?

[B603DC]

How can I grown an email newsletter list organically with no marketing department?

I run a small sales department (b2b), but we have no marketing department. B2B is a tiny portion of our business; we're mostly b2c, but their marketing side doesn't mix with our B2B. I've been given permission to engage in marketing activities, but essentially have no budget (and no control over our website at this point; I will when we start generating more revenue. We're a large company, and B2B only has a tiny piece of the pie at this point.) I've started an email newsletter using MailChimp, and it's been going very well. I have many of our current clients who have signed up, and some leads as well.

How can I best promote this mailing list? I'm using twitter, which has been helpful, but I can't put a link on our website (yet). How else can I market this email list? Any thoughts?

If I can get this to take off a bit, I'm sure I can get some budget next year, but for now, I'm on my own.
Jason - we don't have a store. I work in an office, and we sell to businesses. I have no marketing budget, so therefore I have no giveaways.