For now, he has the best record of any MMA fighter ever. Wins over:
Spratt, Sherk, Trigg, Karo, Mayhem, Hughes x 2, Penn x 2, Serra, Hardy, Koscheck x 2, Fitch, Diaz, Shields, Condit, and Hendricks.
No one has beat so many top 10 fighters consecutively, and nobody even comes close in having beaten so many top 5 fighters. Considering Hughes, Penn were top 3-4 P4P, and that Shields has been the MW champ in SF (with wins over Henderson, Okami, Condit, Lawler...) just ices the cake,
No unavenged losses, most number of consecutive rounds won. With that said, I do think there is a good chance Jones will surpass him. He currently has:
Vera, Bader, Machida, Rampage, Shogun, Teixeira, Belfort, Rashad, Cormier, Gustaffson, Sonnen, under his belt.
That's 11 wins against ranked competition, vs. 18 by GSP. And although Jones has had more finishes, he hasn't been as dominant as GSP was for as long: Jones had a razor close fight with Gus, lost a round or two with Cormier, and arguably lost the first round to Machida. True, he has no losses yet, but he also has beat significantly less ranked competition. I think with three more top 10 wins, he will solidify his position as the greatest ever.
But until now, GSP is simply unmatched in terms of accomplishment.