For me, summer means car trips and lots of them. Our family has gone the portable DVD player route at times, but the kids generally listen to music, read their books, or play Nintendo. But since they were little, we've always had some different kinds of books at hand for when traffic takes its toll or the batteries die.
1) Audiobooks are great for passing the time in the car and feeling like you got some book reading accomplished. I've found that the ones that hold our attention are either funny, adventurous, or familiar. With younger kids in the car, it can be difficult to find the book that works for everybody, so compromise must be employed. Personally, we've had the most success with the Junie B. Jones series. The books are funny, the reader is great, and the stories are familiar. It's also helpful that each book is only about thirty minutes of listening time, so they are perfect for that last hour of a trip when everyone is getting cranky. For older kids, I'd also recommend A Series of Unfortunate Events, read by Tim Curry. Again, these work best when you already know the story as it makes it easier for everyone to follow along.
2) Question books can turn a long car ride into a wonderful opportunity to share stories and memories. Not sure what a question book is? Well, I may be making up the genre as I'm only aware of two such titles for kids, but both are excellent. Ask Me features an interesting photograph or illustration on one page and a question on the other. Questions like, "What do you wish you could do really well?" and "Where do you like to hide?" Another title, Could You? Would you?, by Trudy White features whimsical drawings along with the questions. Sometimes the questions are offered alone, like "Would you like to dance with animals or look at plants?" But many times include follow-up questions or a few ideas to start you off. So, "What makes you smile?" lists pineapple and big goldfish in a pond. Both books are wonderful to start you talking to each other.
3) Find It books are very popular anyway if my library requests are any indication, but a car trip is the perfect place for them. You may buy yourself a reasonably quiet hour only punctuated by an occasional "Found it!" Where's Waldo? series is famous, and the I Spy series by Jean Marzollo isn't far behind. I've also seen these types of books for TV shows and movies, ocean life and museums. I keep one in the car at all times, because you never know when a trip across town can go terribly wrong.
What books have made your car trips bearable?