It has come to my attention through receiving countless email newsletters per week that the ones who never change their template / images at the header - end up not being looked at... There needs to be a constant changing of the content to show new, unique and different content, otherwise people look at the eNewsletter and just think "Same old crapola from this guy" and delete it.
The key to a healthy Newsletter which gets read by more people on the list is new and unique content, things that actually interest them about your area of expertise. The last thing people want to see is a bunch of marketing slogans and a 40 foot long sales message telling them how you are the only one in your industry worth dealing with - let them make that decision - don't try to make it for them!
So what SHOULD you have in your newsletter?
You should be sporting an article of between 200 - 1000 words about something which will benefit your client, include nice pictures (Even if you want to link them to your products) and always end your article with a call to action. "Have you bought your widgets this month? Get a special deal today - go to our webstore and use the coupon code 'SPECIAL' to receive a secret discount on your order!"