I'm aware of instances where "key witnesses" recant decades later (under what kind of pressure from defense attorneys or their own conscience I have no idea...) But I'm unaware of any instances where innocence was clearly established after an execution was carried out.
http://www.innocenceproject.org/know
This strongly suggests that many other innocent people are still on death row or have already been executed, since the Innocence Project doesn't have the resources to investigate all cases of claimed innocence, and has to limit its efforts to saving people who are still alive.
The Wikipedia article on wrongful execution claims that "at least 39 executions are claimed to have been carried out in the U.S. in the face of evidence of innocence or serious doubt about guilt."
Felker and Garrett are the only "specific examples" in that article from the US in the past few decades. Garrett sounds plausibly innocent, but there's certainly no posthumous proof. Similarly, Felker's alibi depends on autopsy results from a body found in a creek. Not really a slam dunk either.
Many anti-death penalty advocates believe (wrongly, I think) that it would be a huge boon to their cause if they could identify someone who was clearly innocent of the crime for which they were executed. oskarth apparently believes instances have already been found. I'm just looking for the current exemplar.
Why post a question like that if you're going to be so intellectually lazy?
Are you too lazy to read before posting a knee jerk Wikipedia page?
How about just posting one name of an executed prisoner?
http://www.newyorker.com/reporting/2009/09/07/090907fa_fact_...