What you want is something that is useful for the people you are sending it to. One of your main targets should be designers as they have a lot of print requirements...so making something useful for them would be ideal.
You could do the standard 'print guide' where it showcases all of your papers etc. But what I thought would be even better is a fun infographic of factoids for designers. Could feature things like appropriate bleed, CMYK values for true black, etc etc. There are a lot of these factoids that junior designers don't know...and could be a nice social media piece and blog entry. You could also print and send to design agencies.
Other content ideas, are on sustainability (your green practices), current clients and how you've helped them (profiles), how to's for designers (more in depth best practices - this could even turn into little videos for a you tube channel).
That's just off the top of my head, but hope it helps! Jeannie x
