I like to have my iPhone or iPad with me so that when there is downtime, I can enjoy some business or personal reading. There are a bunch of apps that use visual media in addition to reading material, which are extremely enjoyable [Al Gore's new book, books by Vook, etc.]
Apps to download and read books and magazines: Kindle, Zinio, Barnes and Noble eReader, Borders, iBooks [Apple's application which will hold both books and pdfs], Instapaper [save online reading for later].
Apps which are themselves to present paper or online magazines: AARP Bulletin, HuffPost, The Economist
Apps which contain reference or classic materials for reading: Holy Bible, Shakespeare, Homer.
[These are mostly apps that contain content on the device rather than always needing to go online to access the data]