The Flash is the Fastest Man Alive in the DC Comics universe. Since his rogues gallery know they can never match him for speed, they must resort to their wits and ingenuity. And it was one such plot that revealed The Flash is so fast... he can't even see himself.
While Wally West (arguably the fastest Flash of them all) enjoys a date with his girlfriend Linda Park, Jay Garrick and Max Mercury find what appears to be Wally's dead body with a note reading, "Dear Flash, you have 60 minutes to stop your own murder, The Suit." Together the three speedsters confirm the dead body is indeed Wally West, and race against time to find out what happened to him, and to prevent it from happening.
'The Suit,' as it turns out, is an actual sentient outfit that once used the criminal Dell Merriwether to perform its crimes. Now a thing of legend, the Suit made its reappearance after being summoned by a spell by two unsuspecting convicts, and teamed up with the time-controlling villain, the Fashioneer (who can be added to the ranks of least intimidating Flash villains ever). Together, the villains scheme to run amok in Keystone City, and eventually freeze Wally in place while setting off an explosion nearby. As a final torment, send Wally's body an hour back into the past with a challenge to prevent his own death.
With the Fashioneer's involvement uncovered, Wally is able to creatively surmise exactly how to prevent his own murder: he creates a time loop! Moments before The Suit freezes Wally in time, the "dead" Wally West awakens, revealing the solution. Changing into his Flash outfit, Wally runs unseen to the explosion in the split-seconds he is frozen in space, but still able to perceive. He then vibrates his past (or, in this case, current) self into a coma-like state of "molecular shock" just as The Suit's explosion goes off. Essentially, The Flash moves so quickly his past, frozen-in-time self couldn't even see what he was doing.
As headache-inducing as this feat sounds, it is par-for-course for the Flash, who recalls Barry Allen telling him "With powers like ours, you often have to learn to fight the way a science fiction writer writes." And seeing as the Flash is able to control the very molecules in his body, to the point of vibrating himself through solid objects, or even outrunning lightning itself, it isn't by any means a stretch to imagine him moving faster than even he himself can perceive. Truth be told, there are more nonsensical questions about the Flash's powers than whether time travel is possible to him, and although this is one solution that stretches credibility a bit, it just goes to show that The Flash is not only the fastest man alive, but also one of the fastest to think of a solution to a problem.