For our adventures, I started collecting travel books years ago...like coffee table books filled with pictures and information about a particular city/state/country, and our collection has grown quickly! It's something we can keep, display in our home, and I love that it's not a normal "souvenir". My favorite part is that I have books written in different languages from our (and others') international travels so it's more authentic, too. Here are a few of my favorites:
these include books from Madrid, Barcelona, Greece, Paris, and Costa Rica
For the girls, we have a standing rule that if Jeff and/or I go to a new place we have never been, we have to bring the minis something home. Not to add clutter to our house, but to incorporate the unique and to teach our girls about other cultures/ways of living/etc. We love the "Goodnight" series books and think they are so so fun...they are wonderful stories jam packed with useful information about each place...the monuments, important details about a particular city, attractions, etc and serve as a great learning tool, too. Definitely something to be on the lookout for when you're away from home.