Here are a few links for learning about Duane Allman's guitar playing:
Video: Duane Allman Lesson
Guitar World's Andy Aledort explains Allman's use of open E tuning, and demonstrates some Allman-style licks over Statesboro Blues. Video: Duane Allman Licks
This YouTube video demonstrates a few of Allman's classic riffs.
10 Things You Gotta Do to Play Like Duane Allman
There are no specifics here - you're not going to learn any licks. But this Guitar Player article is a fun read.
Duane Allman's Gear
Allman was fond of vintage instruments, so trying to reproduce his sound might cost you a pretty penny. This post on the Gibson web site explains some of Duane Allman's favorite instruments.
Poll:Should Duane Allman Be On This List?