Okay, here are the answers! Thanks to everyone who took part - I hope you had fun trying to figure them out!
Congratulations to everyone who got these right, and especially Lizzie Loves Pancakes for guessing the most correctly.
** 1 **
'Life, the Universe and Everything' by Douglas Adams - book three of the Hitchhiker's Guide to the Galaxy series.
** 2 **
The movie 'The Haunted Mansion', starring Eddie Murphy. This line is actually from the blooper reel.
** 3 **
'Les Miserables' - Javert sings "I am the law and the law is not mocked!" in his suicide song.
** 4 **
'The Phantom of the Opera'. Original lyrics "He's here, the phantom of the opera!", etc.
** 5 **
'Mulan 2', line said by Princess Mei.
** 6 **
'Wizards of Waverly Place' - often said by Jerry.
** 7 **
'Scrubs' - JD sneak hugs Dr Cox
** 8 **
'Twilight' - originally lion and lamb
** 9 **
'Sherlock Holmes' series by Sir Arthur Conan Doyle
** 10 **
'John Tucker Must Die' - possibly Kate's most famous line
** 11 **
'Harry Potter and the Philosopher's Stone' - first conversation between Harry and Ron
** 12 **
'The Wixard of Oz'
** 13 **
'Phineas & Ferb' - well known saying from the show
** 14 **
'The Lion King'
** 15 **
Any version of 'The Nutcracker'
** 16 **
'Mort', part of the Discworld series by Terry Pratchett
** 17 **
Volume 3 of the manga '+Anima' - Husky says this when Nana gets worried about where Cooro might be
** 18 **
'Shrek'
** 19 **
This was possibly the most confused one.
'WALL-E' - the scene when EVE and WALL-E exchange names, and WALL-E insists on calling EVE 'Eve-a'.
** 20 **
'The Poison Belt', from the Professor Challenger series by Sir Arthur Conan Doyle.
** 21 **
An episode of 'iCarly'
** 22 **
'101 Dalmations' - a reworking of the song 'Cruella de Vil'
** 23 **
'Animorphs' series by K.A. Applegate - every book starts off in this style