Turn Back the Years: The Essential Hank Collection (2005)
This is the latest from Lost Highway Records, Williams' official distributors. The three-disc set includes rare photos and an essay by one of Williams' many biographers.
Three Hanks: Men With Broken Hearts (1996)
The son and grandson team up to record their own voices over old recordings of Hank Sr.
20 of Hank Williams' Greatest Hits for iTunes
It is what it sounds like, and it should be a good place to start.
Lost Highway: A Tribute to Hank Williams (1999)
Various big-shot singers cover Hank's big-name songs.