Anderson, Chandler, de Camp, Harrison, Piper, Vance.
Hans
I've not read Anderson nor Chandler, what I've read of de Camp screams "D&D started here" but looks nothing at all like Traveller, Harry Harrison I can see some, but nothing strong enough to be more than genre reference...
HB Piper is clearly an influence on Traveller, but the books don't feel at all like traveller to me. There are bits lifted... but the feel was very different.
And Vance feels nothing at all like anything I've played in gaming. I can see how Gygax pulled inspiration from the magic, especially Rhialto, but Ugh... I can also see almost all of what I consider Gygax's worst advice to GMs seems to be an attempt to out-Vance Jack Vance... I found volumes 3 & 4 of Dying Earth particularly unpleasant. If I was playing in a game with a GM trying to emulate those, I'd tell him to do anatomically impossible things, and walk away.
EE "Doc" Smith is also a strong influence on some people's Traveller games... and the description for the Special psionic power clearly hints at Lensman.