Shaun Tan's (ALMA 2011) site is full of interesting information and news: www.shauntan.net. His new (July, 2012) blog is available here. Sonya Hartnett's (ALMA 2008) site contains not only information about the author and her works, but also teacher's nots for several of her books.
Katherine Paterson's (ALMA 2006) site has been named after her most famous book, you'll find it at Terabithia.com.
Ryoji Arais (ALMA 2005) site is mostly in Japanese, but even if you don't read Japanese, you can still enjoy the large display of his artwork. All you want to know about Philip Pullman (ALMA 2005) you will find at philip-pullman.com.
Lygia Bojunga (ALMA 2004) started a publishinghouse with the help of the award money. More info on Casa Lygia Bojunga.
Banco del Libro (ALMA 2007) and The Tamer Institute (ALMA 2009), the two organisations that have so far received the award, have official websites.
Christine Nöstlinger (ALMA 2003) does not have a website yet.