The Smithsonian has the most beautiful online library of vintage seed catalogs, and we've been using them to make envelopes of all sizes. All you need is a color printer (doesn't everyone have one of these now?), scissors, glue stick, a pen and seeds.
Here is the site: http://www.sil.si.edu/digitalcollections/SeedNurseryCatalogs/collection.cfm
Also, download the HOMEGROWN Seed Packets available under the show and tell tab! http://www.homegrown.org/page/homegrown-howto-cards-steal