Write, Click, Scrapbook shows some ideas for making calendars in a post here. There is also a free download available.
Here is a nice calendar from StorybyMia's Etsy shop.
This is a neat idea to make for a wall calendar. See it on Pinterest here.
This idea, shown on Design Sponge, looks like something that could be recreated quite easily.
This Old House shows how to make this calendar using chalkboard paint here.