I have one that I use every week. I don't know that it is great, but your welcome to use it. If you could send me your email address, I'll send it to. I don't have it on my home computer, so I'll have to send it from school.
I use Microsoft Word and make a schedule for all subject areas and what the students will be learning. I put my "news" at the bottom. It looks a lot like my plan book in the box areas (I insert a table via M Word). The students and parents (and subs) can usually follow it very easily. I save the table and then just delete and add new information each week. For each subject area (such as reading) I can list target words, story, skill, etc. I can also list when quizzes and homework will fall.
I too use a template from Mailbox Magazine which I can fill out on-line. I love that I can do this on-line! I can copy it to Word Perfect to spell check and then make any changes with spelling or typos. I do one or maybe two a month and usually on the flip side is my monthly homework calendar which I now create myself in Word Perfect using a table grid. Now that I have a rhythm it is pretty easy for me. I couldn't justify making a weekly newsletter/homework sheet as that would be too timely for me and way too much paper used in my school! The once a month, occationally twice a month, is just right for the needs of my classroom.
I'm sure someone in your school would have an old copy of a mailbox template that you could use to do one by hand to start or you might look into using the site if you have the money or see if the school can pay for it. If your school Librray subscribes then there should be some way to log on and use these resources. Couldn't hurt to ask.
If you are looking for a template already made in word, you can google "Kelly's Kindergarten". She has two templates for most months of the year! You can type right in those boxes! Simple, looks good and saves you time! Have fun! She also has a lot of other neat things like lables for manipulatives.