A Card a Day by Leisure Arts Publications:
"Just as greeting card shoppers spend time selecting a card that best reflects their personality and that of the recipient, paper crafters like to browse for inspiration to create a handmade card. That's why Paper Crafts magazine editors have gathered more than 365 card ideas, making this book the ultimate resource for inspiration, design, tips and techniques. Like a yearly calendar, the book is divided into months, to guide card makers through tons of new ideas for every occasion imaginable. There also are helpful sections on basic tools and supplies, using color combinations, and hints for basic organization and storage, as well as dozens of sketches for all shapes and sizes of cards. "
And you'll need an envelope as well....
Pushing the Envelope by Marthe Le Van.
From the publisher, Lark Crafts:
"So often we focus on what’s in the envelope, we forget the envelope itself. But this collection embraces the envelope as a creative form. Devised by a group of talented designers, these unique handmade envelopes come in all shapes and sizes. Some involve embellishing commercial envelopes with surface treatments, such as stamping. Others require folding techniques, and a few use unconventional and recycled materials. There are projects for packaging CDs, photographs, gift cards, and more."
(Over the Counter is a regular feature at A Bookworm's World. I've sadly come the realization that I cannot physically read every book that catches my interest as it crosses over my counter at the library. But... I can mention them and maybe one of them will catch your eye as well. See if your local library has them on their shelves!)