YouVersion Online Bible Devotional Readings - This site lists a wide variety of daily devotional reading plans. It is one of the best sources for Scriptural daily devotional readings. Some of the plans look at Scriptural teachings on a given topic, some take you through certain parts of the Bible or deal with certain Bible characters, and some give you a big picture view of the Bible.
Crosswalk.com – scroll down a bit on the page to see a list of popular devotional links.
OnePlace.com – a variety of devotional readings from dozens of writers and ministries.
My Utmost For His Highest by Oswald Chambers – a classic daily devotional reading
Our Daily Bread – a time-tested source for daily devotional wisdom and insight
Morning and Evening by Charles Spurgeon – another classic daily devotional reading. This site has the option of listening to each daily entry.