There are quite a few apps specifically for the lawyer or litigator. If you search online you'll find quite a few blogs or websites on the topic of apps for lawyers, office practice and in litigation or on appeal. And some provide text of materials that are useful. Many apps are for the iPhone/iPodTouch, but either also apply to the iPad or can be made to do so:
Constitution, Declaration [of Independence], Your Rights, Wierd Laws
Law Stack, LawBox, Law Dictionary
FastCase [for access to caselaw on the iPhone or iPad.