At Cyberwalker, we use Constant Contact.
We send material to our members once a month.
This material consists of (1) video newsletter (tech related) and (2) a coupon newsletter to software (also tech related - usually security orientated) that we have arranged to offer a discount to our readers.
With both of these, we give the member an option to sign up to receive both, just one or none.
I try to spread both types of emails to b sent every two weeks. This way the member doesn't feel they are getting spammed.
I hope this answers your questions. If not, feel free to PT or email me.