Here's a list of some great classic rock artists somewhat similar to Hendrix and Led Zeppelin. I also put some songs by each artist you might want to start with in parenthesis).
-The Who (especially "Won't Get Fooled Again","I Can't Explain", and "My Generation")
-The Rolling Stones (especially "Gimme Shelter","Under My Thumb", and "Sympathy for the Devil")
-Creedence Clearwater Revival (especially "Down on the Corner","Up Around the Bend", and "Fortunate Son")
-Blue Oyster Cult (especially "Don't Fear the Reaper" and "I'm Burning for You")
-Jethro Tull (especially the entire album "Aqualung")
-Rush (if your new to them, you might want to start with something like "Limelight" to get used to Lee's singing style)
-Van Halen (especially "Panama" and "Ain't Talkin bout Love")
-Aerosmith (anything on their greatest hits album)
-U2 (especially "New Years Day" or "Sunday Bloody Sunday"
-AC/DC ("Back in Black" and "Highway to Hell" are both essentials)
-Boston (you'll want pretty much their entire debut album, especially "More than a Feeling", "Peace of Mind", and "Foreplay/Longtime")
-Queen (especially "Under Pressure" and "Don't Stop Me Now)
-The Doors (especially "Light my Fire" and "Break on Through")
-Cream (anything/everything off Disraeli Gears)
-Guns N'Roses (especially "Sweet Child of Mine", "Welcome to the Jungle", and "Yesterdays")
-Steppenwolf (especially "Born to be Wild", "For Ladies Only", and "Hey Lawdy Mama")
-Deep Purple (especially "Woman from Tokyo", "Hush" and obviously "smoke on the water")
-Black Sabbath (especially "War Pigs)
-Neil Young (especially "Cinnamon Girl" and "Ohio")
and nobody get offended that I left off many other great songs by each artist, I only listed a few suggestions from which he can begin to explore each artist (if he hasn't already)
