The Louise Rennison books are brill (my husband loves them). You could also try books by Echo Freer (Magenta Orange is a very funny character - three books about her; Magenta Orange, Magenta in the Pink and Magenta Goes Green, also Blaggers and Diamond Geezers, which both have hilarious gangster twists, but have very sassy heroines), and Meg Cabot (1800-Missing, Mediator, Princess Diaries, Teen Idol are all good, wholesome but credible reads).
Hilary Mackay has a lovely series of books about the Casson Family - Saffy's Angel, Indigo's Star, Permanent Rose and Caddy Ever After - they're the family of a seperated artist couple who are all just trying to muddle through a hectic life. Fun, sweet and with a wholesome message about love being the most important thing that families have.