At my school, we provide each grade level of students a list of books and ask them to choose and read one book from the list. Our summer reading list looks like this for 2013:
All the Lovely Bad Ones by Mary Downing Hahn
Tears of a Tiger by Sharon Draper
Mockingbird by Kathryn Erskine
Legend by Marie Lu
Greetings from Nowhere by Barbara O'Connor
Shug by Jenny Han
This is for incoming 7th graders. We typically announce the list to students in the last few weeks of school, and we visit classes to promote the books and encourage students to read over the summer. (I did a survey about this a few years back, and I found that other than the obvious factors - like access to the books - the single biggest predictor of whether a kid read over the summer or not was if a teacher encouraged him/her to do so. These talks make a big difference.)
We put a lot of thought into this over the years, and I think that our students benefit from the narrow list of choices that (hopefully) includes at least one reasonably appropriate book for them. We try to diversify the list so that virtually every reading niche can be filled. For example, Shug is kind of a "girl" book. It's a realistic fiction novel about a young woman who is in love with her (male) neighbor and former best friend, and who deals with the awkward realization that he might not like her in that way, but still want to be her friend. Legend is either a "nerd" book or a "boy" book, depending on how you spin it. It has a lot of sci-fi action (and some romance - don't tell the boys). We also try to level the books appropriately. All the Lovely Bad Ones is a 670 Lexile or about a 5th grade reading level. It's also less than 200 pages long. Legend is slightly higher-level in terms of text complexity, but the subject is more difficult to comprehend and requires more abstract thinking (dystopian future). It's also 330 pages. Mockingbird is deceptively simple: it's told from the perspective of a girl with spectrum disorder, and requires a lot of careful, inferential reading to understand events through her distorted filter. It can be a difficult (but rewarding) read.
My son's district sends a list of state award nominations and asks students to choose and read a book from these lists. There are many more choices, but it would be more difficult for teachers to keep up with such a long list, and almost as difficult to connect these books to some kind of classroom learning once summer is over. I think that would be less useful for us. Our area high school has a single title that is "required" summer reading for incoming freshmen. This allows for a series of assignments or classroom activities connected to this book, and I'm sure that the high school knows and teaches the book very well, when everyone is asked to read the same thing. But it also reduces the opportunity to differentiate (or let students self-differentiate), and it allows for less engagement and "buy-in," since the students are all being forced to read the same thing without regard to interest. (And what if they've already read the book?)
So, I think the program should reflect the purpose. Our ostensible purpose is to have kids continue reading over the summer to reduce losses in fluency and/or reading comprehension. Over the years, most of the reading teachers in the building have developed other ways to employ the summer reading, from "book talks" to the class, to creating products about these books, to mini "book groups" around the selected summer reading book, to "book trailers." I typically prefer to use summer reading books to dive right into teaching effective collaboration and discussion, group work procedures at the beginning of the year, and as a way to informally assess interest and reading level early in the year, before much of the initial testing data is available.
Finally, I also have to admit that I really enjoy "shopping" for summer reading titles, and I've been known to make wild suggestions to throw out the whole list and start over. We experiment a lot, and we often pull titles from the Rebecca Caudill list for our summer reading. Most of the titles on our list came from the Caudill nominations at some point or other, a list that I am again trying to read in its entirety. I am getting ready to discuss the books with 6th graders tomorrow - let's hope it goes well!