Biblegateway.com is a fantastic site for general reading and study. It offers various versions and some study helps.
Blueletterbible.org is a commentary site with free access to an abundance of commentary and other aids.
Preceptaustin.org is a site that has done the bulk of studying for you. Simply search the book your interested in and you'll find a great deal of information on that book.
Youversion is a fantastic Bible app for your mobile device.
Logos Bible Software is one of the most powerful Bible study tools available.