BOC has good stuff, but the albums usually leave something to be desired. Secret Treaties is their most complete, followed by Tyranny and Mutation, but the first 4 are all worth a spin or two.
I forgot Kyuss - Blues for the Red Sun. Great album and the only one from Kyuss I own. Could have something to do with my "lifestyle activities" when I was into that album...
The best Allman Brothers album is Live at the Fillmore East. Essential listening and the quintessential southern rock album, but I didn't include it since it is a live album. That's where southern rock shines in my opinion, live. It's a mix of rock, blues, country, and jam band.
As for hard rock, I guess I should have read the thread title better. I wouldn't include these in that category (which I thought was just rock but I guess the line gets blurry pretty quick. My bad)
The Cars - The Cars
Boston - Boston
Blue Oyster Cult - Secret Treaties
The Black Crowes - Shake Your Money Maker
Dire Straights - Brothers in Arms
INXS - Kick
Pink Floyd - Wish You Were Here
U2 - The Joshua Tree
Weezer - The Blue Album
And oh yeah, I agree that punk should be in a category by itself.