Driving-Tests.org and DMVCheatSheets.com offer state-specific driving guides and online practice tests. As of January 2016, Driving-Tests.org provides free practice tests, but DMVCheatSheets.com is a fee-based service that charges separately for guides and practice exams.
DMVCheatSheets.com offers materials for car, truck, motorcycle and learner's permit tests. Their guides include 50 questions with information explaining the different parts of a state’s driving test, including sections that cover signs and the consequences of driving under the influence.
Driving-Tests.org has many tests for each state, including rules of the road, signs, fines, limits and regulations. Practice tests explain the driving principle for each answer and are available in Spanish.