I usually have a four step approach to “commentaries.” I start with linguistics and cross references and work my way down until I am out of time or have enough. http://www.preceptaustin.org/ has lots links to resources in all catagories and information about how to study the Bible.
This is all free stuff online or downloadable. I put links on here because it is a helpful resource for me, not because I endorse the organization that makes it available. Check out the web site (doctrinal statement, links, sponsoring person or organization) or Google the person to find out more about them. The important thing is that you understand the perspective and orientation of the source. Be aware of who you are using.
Linguistic/language
Versions, many with audio http://www.biblegateway.com/
NET Bible, I’m not a big fan of the translation but love the copious translation notes
Blue Letter Bible has good word study and grammar identifications/explanations
Download Greek / Hebrew interlinear Bible Software http://www.scripture4all.org/
Online study tools with helpful Greek and Hebrew concordance feature http://www.biblestudytools.com/
Tons of cross-references in the Treasure of Scripture Knowledge
Vine’s Expository Dictionary of the New Testament
Robertson's Word Pictures of the New Testament
Vincent’s Word Studies
E-Sword has Keil and Delitzsch, 10 volume commentary on the OT which deals with a lot of OT textual issues, as a free module
History/culture
Alfred Edersheim is good on OT Bible history and the Gospels http://philologos.org/online.htm#Edersheim
Locations by Bible chapter with Google maps and ISBE articles http://www.biblemap.org/
International Standard Bible Encyclopedia 1915
Web Bible Encyclopedia is a good place to look up names, etc..
http://christiananswers.net/dictionary/
BlueLetter Bible multiple dictionary look up page http://www.blueletterbible.org/search/Dictionary/viewEntries.cfm?Letter=a&TwoLetter=an
Doctrinal
I recommend Dr. Constable's Expository (Bible Study) Notes http://www.soniclight.com/constable/notes.htm
Lots of articles and commentaries, most scholarly http://bible.org/
Barne's Notes on the New Testament http://www.studylight.org/com/bnb/
Charismatic, but still very good David Guzik's Enduring Commentaries on the Bible http://www.enduringword.com/library_commentaries.html
Dispensational general commentaries, misc. http://www.biblecentre.org/
Lots of old and ancient resources http://www.ccel.org/
Classics: Calvin, Darby, Geneva, Gill, Jamieson-Faussett-Brown, Matthew Henry, Wesley http://www.ewordtoday.com/comments/
Lots of stuff on David Cox's Online Religious Library http://www.davidcox.com.mx/library/library.htm
2,800 word vocabulary commentaries that have all the cookies on the lowest shelf http://www.easyenglish.info/
Devotional/Homiletical
Paul Apple details lesson notes with good insights http://bibleoutlines.com/library.html
Matthew Henry is not dispensational, but has tons of good applications. http://studylight.org/com/mhc-com/
Spurgeon sermons are helpful for developing a homiletic strategies for your text http://www.spurgeon.org/mainpage.htm
http://www.oneplace.com/ has a wealth of popular teachers and preachers (living and dead) from a variety of backgrounds
Skeptic’s Annotated Bible helps to anticipate criticisms of the Bible text http://skepticsannotatedbible.com/
This is all free stuff online or downloadable. I put links on here because it is a helpful resource for me, not because I endorse the organization that makes it available. Check out the web site (doctrinal statement, links, sponsoring person or organization) or Google the person to find out more about them. The important thing is that you understand the perspective and orientation of the source. Be aware of who you are using.
Linguistic/language
Versions, many with audio http://www.biblegateway.com/
NET Bible, I’m not a big fan of the translation but love the copious translation notes
Blue Letter Bible has good word study and grammar identifications/explanations
Download Greek / Hebrew interlinear Bible Software http://www.scripture4all.org/
Online study tools with helpful Greek and Hebrew concordance feature http://www.biblestudytools.com/
Tons of cross-references in the Treasure of Scripture Knowledge
Vine’s Expository Dictionary of the New Testament
Robertson's Word Pictures of the New Testament
Vincent’s Word Studies
E-Sword has Keil and Delitzsch, 10 volume commentary on the OT which deals with a lot of OT textual issues, as a free module
History/culture
Alfred Edersheim is good on OT Bible history and the Gospels http://philologos.org/online.htm#Edersheim
Locations by Bible chapter with Google maps and ISBE articles http://www.biblemap.org/
International Standard Bible Encyclopedia 1915
Web Bible Encyclopedia is a good place to look up names, etc..
http://christiananswers.net/dictionary/
BlueLetter Bible multiple dictionary look up page http://www.blueletterbible.org/search/Dictionary/viewEntries.cfm?Letter=a&TwoLetter=an
Doctrinal
I recommend Dr. Constable's Expository (Bible Study) Notes http://www.soniclight.com/constable/notes.htm
Lots of articles and commentaries, most scholarly http://bible.org/
Barne's Notes on the New Testament http://www.studylight.org/com/bnb/
Charismatic, but still very good David Guzik's Enduring Commentaries on the Bible http://www.enduringword.com/library_commentaries.html
Dispensational general commentaries, misc. http://www.biblecentre.org/
Lots of old and ancient resources http://www.ccel.org/
Classics: Calvin, Darby, Geneva, Gill, Jamieson-Faussett-Brown, Matthew Henry, Wesley http://www.ewordtoday.com/comments/
Lots of stuff on David Cox's Online Religious Library http://www.davidcox.com.mx/library/library.htm
2,800 word vocabulary commentaries that have all the cookies on the lowest shelf http://www.easyenglish.info/
Devotional/Homiletical
Paul Apple details lesson notes with good insights http://bibleoutlines.com/library.html
Matthew Henry is not dispensational, but has tons of good applications. http://studylight.org/com/mhc-com/
Spurgeon sermons are helpful for developing a homiletic strategies for your text http://www.spurgeon.org/mainpage.htm
http://www.oneplace.com/ has a wealth of popular teachers and preachers (living and dead) from a variety of backgrounds
Skeptic’s Annotated Bible helps to anticipate criticisms of the Bible text http://skepticsannotatedbible.com/