John Piper's series: Hebrews: The Radiance Of His Glory - This is 54 talks (473mb) that he gave in 1996-1997. The first three talks started off from his Easter message, but then decided to spend the rest of the year and then some going through Hebrews. You can download or read the transcripts for free.
Kent Hughes on Hebrews (under the series drop down select Hebrews)- This is 47 talks (365mb) he gave in 1991-1992 to his church. Later he turned this into a two volume book. All these talks are free as well.
Tom Wright - Hebrews for Everyone - I haven't read much of what Tom Wright has directly written, I have only read second hand from others telling me about what Tom Wright has said. I'm hoping he will give some good historical background to the text in a nice easy to understand way. I am keen to read this and want to see if he will put Hebrews into an Exile/Return to the Kingdom type theme.
The Message of Hebrews - My wife has a fair few of The Bible Speaks Today commentaries. I have only read one of them before and they more seems like a devotional book than a commentary. This hopefully will help with practical application of the text.
e-Sword - This has old school commentaries by Albert Barnes, Adam Clarke, John Darby, John Gill, Matthew Henry, John Wesley and a fair few more as well as a few dictionaries. All this should shed some light on the text. This is also free.
Wikipedia - This also has some good historical points and comments on related articles about Hebrews.