Professional newsletter editor, publisher, and layout artist here.
I think the key isn’t necessarily finding a template, or using a particular program, but learning and applying the basic principles of graphic design. Pick up some books or visit some Web sites on the subject. Look for newsletters you find attractive and emulate (i.e., steal from) them.
It’s getting late, so I don’t have time for a full-blown master class right now (not that I’m really a master designer, anyway), but here are a few basic rules to apply and beginner’s mistakes to avoid.
Pick a handful of attractive fonts that work well together and stick with them. One or two body fonts and three or four display fonts for headlines are all you need. DO NOT use a different font for every article or every headline. Absolutely nothing screams AMATEUR DESIGNER more than a four-page newsletter with 16 different fonts.
On the subject of fonts, your main body typeface should be a proportionally-spaced serif font. Except for short pieces, sans-serif fonts are hard to read. You can use them for sidebars or other short pieces, but don’t use them for full-length articles. Just don’t!
Conversely, headline and display fonts should be sans-serif. Avoid overly ornate or script faces, except for those rare occasions where it is appropriate to the subject matter. And even then, be careful. Using all caps in most script fonts is virtually unreadable.
Leave enough white space in margins, between columns, and around pictures. A page crowded full of text appears daunting and discourages readers. If you don’t have an image to go with an article, use pull quotes to break up the page.
Page layout within each issue and across issues should be varied, but consistent. Simple and functional is much preferable to flashy and unreadable. (Would that more Web designers followed this precept!)
There are several million other “rules” but this will do for now.