Cantor's Deli, especially in the Kibitz Room lounge/bar/club which is a hangout for musicians and some of the Hollywood crowd. (...of course, late night is better than lunch here...)

Musso & Frank Grill is ***old*** Hollywood, and the place serious players come to do deals in the back booths. I still remember my grandfather (a studio accountant & 2nd unit manager) taking me there in the 1970s... The waiters knew everyone's names....what they liked....and knew all the gossip.