Confessions of a Shopaholic, by Sophie Kinsella
It's been ages since I've read this, so I can't recall a single joke or excerpt that made me laugh--but I know it did, because I still remember sitting on my couch with it after a long, horrible day and laughing out loud so much, I forgot everything but being happy. So, thank you for that, book. I owe you one big time.
The best part is--this is a series! I've read the second (also ages ago) and just bought the third. I'm feeling a reread coming on. ;)