In addition to the audio, I have also found a couple of helpful resources on Messiah. First, there is a free guide online that provides you a "worship map" of the performance. The worship map provides you the major parts, lyrics and scripture references to help you move through the entire score. Also, another helpful guide has just been published in book form, Handel's Messiah: Comfort for God's People. The publisher states:
Here you will find fascinating historical background to Messiah, including its unlikely inception, and learn about its reception and impact from Handel's day to our own. Calvin Stapert devotes most of his book to scene-by-scene musical and theological commentary on the entire score, demonstrating how the music of Messiah beautifully intertwines with and illuminates its biblical text. Through these pages Handel's popular and much-loved masterpiece will be greatly enhanced for listeners old and new alike.You can find a free Google preview of the book here.
If you don't have the time or desire to read the book, then you can simply download it and listen to it. For this month, ChristianAudio.com is graciously providing it as a free download [HT: Jame Grant]. To download the book, you simply have to go here and click on "Download Now."