If you're looking for a good laugh, check out Postcards From Yo Momma. This website doesn't collect postcards in the traditional sense — these aren't handwritten snail mail cards with a pretty picture on the front. Nope, these "postcards" are actually emails from mothers to adult children, and they're hilarious and kind of sweet (well, most of them). After finding amusement in their own mothers' emails, editors Jessica Grose and Doree Shafrir began collecting emails from mothers around the world. A compilation of these missives will be published in their book, Love, Mom: Poignant, Goofy, Brilliant Messages from Home, which will be out on April 1st.
Below are some links to some travel-related "postcards"; you'll find many more on the site: