Book boxes (shoe box sized) in each classroom with fiction themed around the subject would be great and displays in classrooms of themed fiction would bring even more books into the school - would have liked some in the PE changing rooms especially! On the subject of display, wordclouds (created with Tagxedo.com) of relevant subject specific vocabulary would be great as well as posters advertising fiction titles available related to particula
Perhaps a whole school focus on one aspect of grammar each term, connectives for example would work with students given a score card to collect points/stars each time they showed good use of the particular focus in any subject. It would be wonderful to have a word of the week with an emphasis on every teacher trying to use the word at least once in a day - words would have to be carefully chosen of course!
For primary I'd like to survey the children and find their favourite animals then create a 'book zoo' with themed books (Charles Tiger, There's a Hippopotamus on our Roof Eating Cake, Greedy Zebra, Tiger that came to tea for example). A large map of the world near by with pins where the various animals live would be cool and again I'd like to use sound clips with animal noises on this.
To encourage more writing in subjects blogging can't be beaten in my opinion, whether that be long blog posts or micro blogging like Twitter. If each department had a blog , a couple of students each lesson could be chosen to write a short blog about the lesson and relevant subject news , such as new scientific discoveries could also be showcased.
When it comes to apps there are several that spring to mind that could be used in several departments - Unwanted Guest (PSHE, Media, Art, English) , War Horse (English, History, Drama) and Anne Frank (History, English, Geography.)
Just some first thoughts.......if you try any of the ideas please do let me know if they work!