My brother uses Constant Contact and MailChimp. Keep in mind he's not a spammer and sometimes when folk ask about a campaign, they mean spam. Don't try to hide it when you want to spam since how to spam is well, you can google how today.
I'm using Mailchimp too for some clients of mine. With the free account you can do already quite alot. If you're not familiar with (properly) coding your own HTML emails/newsletters there are loads of templates you can choose from. Campaign Monitor is another great email marketing service.
There are also email frameworks which you could use to create your own templates if you don't know how to do that with proper HTML (table layouts). With these frameworks you use custom markup language to create your layouts and then generate the HTML to import into Mailchimp or Campaign Monitor.
MailChimp is one of the most popular and easy email creator. It is the best email marketing software for nonprofits. Very easy, great tools and awesome support. They offers a forever free plan which allows to send 12,000 emails for upto 2,000 subscribers.