Steve Martin - admittedly, I was 7 at the time but the tv special where he drove the steamroller drunk and sang in the cowboy bar full of chimps was my first memory of laughing so hard that I was in pain.
Cosby - although my firsthand experience meeting him turned me away from him (hear the story in the archives!), I cannot deny his influence on me.
Eddie Murphy - Delirious - me and my brother listening to this LP in secret in the garage and trying not to laugh too hard for fear of getting busted listening to r-rated material. It made it that much sweeter.
Those were the big three, but there were many others that I can say that I did, or do still enjoy: Richard Jeni, Drake Sather, Norm McDonald, Rodney Dangerfield, Steven Wright, Dennis Miller. Some 'newer' folk: Patton Oswalt, PFT, Birbiglia, Cross, Dave Attell, Greg Giraldo...
I will always hold a special place in my heart for the guy who played the flamingo-shaped electric guitar.