I read Adam Rex's The True Meaning of Smekday a week or so ago, and enjoyed it very much. (Thanks to jadelennox for the recommendation!)
"The True Meaning of Smekday" is (within the novel The True Meaning of Smekday) an essay written by Gratuity "Tip" Tucci (her mother started calling her "Turtlebear" once she found out that "Gratuity" didn't mean what she thought it meant when she named her daughter). The essay was occasioned by the "National Timecapsule Project" to "provide a record of this time in American history for generations to come". "This time in history" meaning when the extraterrestrial Boov invaded on Christmas Day (which they renamed Smekday in honor of their glorious leader Captain Smek) 2013.
Gratuity, who is eleven-and-a-half for most of the events recounted
in the book, is caught up in the central events of the time. Before
the invasion, her mother claims to have been abducted by aliens (and
forced to fold laundry), has a large and growing (and glowing!) mole
on her neck, and then disappears on Christmas
DaySmekday. Gratuity survives on her own after the Boov
invasion (and destruction of all human resistance), but when the Boov
discover that humans are unwilling to let the Boov move into their
cities, the Boov decide to put all humans into small areas
(Americans get Florida). Gratuity decides to drive to Florida rather
than go in the Boov rocket pods. Hijinks and hilarity ensue.
I could summarize some of the plot, but it would probably sound like a ten-year-old describing their favorite movie to someone who has never heard of it. Suffice it to say that it's an enjoyable romp, complete with irony and wit, some of which would go right over the heads of younger readers (and that's okay). And it includes one of the most twisted explanations of how Disneyworld (showing up here as "Happy Mouse Kingdom") manages to stay so incredibly clean.
The cast of characters includes Gratuity's mother's cat (named "Pig"), a Boov who calls himself "J.Lo" and is on the run from the other Boov, more aliens (the Gorg), and a bunch of pre-teen boys hiding out in Happy Mouse Kingdom, who have formed "the Brotherhood Organized Against Oppressive Boov" (BOOB). (Gratuity asks if that shouldn't be "BOAOB", but the boys reply that they wanted to be "BOOB". Needless to say, this doesn't endear them to Gratuity.)
The book is illustrated with near-realistic drawings (representing the Polaroids that Gratuity takes), Gratuity's drawings, and a couple of comic strips drawn by J.Lo to explain various things Boovish. Adam Rex is ridiculously talented to be able to draw all these things and write as well as he does. (Not fair!)
You should also look at www.smekday.com, which includes a short "Human Learning Video #42: The True Meaning of Smekday" (if the Quicktime movie doesn't work for you, follow the link to the YouTube version). This instructional video is of a puppet show explaining the new Boovish holidays, and is one of the funniest things I've ever seen. (I was nonplussed the first time, and every viewing since it just gets funnier.) The problems (for me) with the video are (a) it raised my expectations too far -- no book could include the sheer density of comic genius that the video does; and (b) there's only one!
In summary: go buy this book. It's fabulous (and on sale at Amazon). And watch the video.