If your comic has an opt-in reader email, or if you have a blog allowing email subscriptions, have a look at Ezine Directory.
It's a human-edited list of publications which arrive regularly by email. Comics are among the categories, and the comics list is very thin, so it should be easy to get some attention.
You can also browse, rate and organize the listings by ratings and popularity.
We've all received newsletters we don't want and can't stop, but plenty of sites use opt-in newsletters (with easy op-out) as a way to enhance the creator-reader experience.
Most articles I've seen about newsletters are dull affairs, rambling about the importance of bombarding your customers with news about your handmade parakeet swings.
An article to dedicated readers about big news regarding your comic is another matter. Whether you work in a tasteful merchandise mention is your call.
I don't think you should do a newsletter if you're not a writer used to writing like a journalist, with word compression and tight editing. Or, if you have a good editor -- that works. If it's funny and has good art and design, now you're talking.
I have no plans for a newsletter, but I published a lot of zines before the internet. If you do a stand out job, you will earn loyalty. If it's more of an afterthought, it isn't worth the bother.
Ezine gives you a chance to increase your reach if you do have one.
