A player that I am familiar with due to his two year stint with the Brewers. Marcum came to the Brewers in a trade during the 2010 off season for Brett Lawrie as they were pushing to make the post-season (which eventually resulted in a NLCS trip).
While he did struggle in the post-season, I think he was trying to pitch his way through an injury as his pitches didn't have the same kick to them. Still, I do have positive memories of him pitching for the Brewers as he did pitch well in the 54 starts he had over the last two years.
His 2013 season with the Mets was a whole different story as he had further injury issues and had his worst season over the 14 games where he was healthy. I think he can get past his struggles and would be a good buy-low option for someone looking to fill out the back end of their starting rotation.
The most similar player to him through age 31 was Bob Walk. After turning 31, he had plenty of innings left in the tank (even if they weren't that great) as he pitched at least 115 innings in his age 32-36 seasons though Walk's career ending less than ceremoniously with him leading the league in earned runs allowed in 1993.
Another player that is coming off an injury shortened season. While Karstens had a better season than Marcum, overall career performance indicates that he doesn't have as much upside as Marcum. I think he'll find his way back in the bigs but he'll probably get a minor league deal and successfully compete for a #4 or #5 starter job during spring training. You could do better but you could also do worse.
Also, he is still young and maybe he is a late bloomer, it wouldn't be unprecedented. His most similar player through age 29 is Mike Scott. Coming out of his age 29 season he was just another below average pitcher that somehow kept getting work but little did anyone know he was two years away from leading the league in Strikeouts, ERA+, WHIP & Hits per Nine innings. While the odds are highly stacked against Karstens ever being in the Cy Young award discussion, he may be a good value for whoever signs him.
Even with the knowledge that the performance of relief pitchers can be very fickle and subject to small sample size, i'm pretty surprised that O'Flaherty hasn't been picked up. Before doing research on this posting, I didn't quite realize how consistently good he has been (even if 2013 was shortened by injury). He's had an ERA+ of at least 136 over the last five seasons and was virtually uninhabitable in 2011 & 2012. Depending on where he ends up, he could be one of those players that picks up a closing gig and help fantasy owners everywhere get an advantage in the saves category.
His most similar pitcher through age 28 was Craig Lefferts which seems a bit odd as while Lefferts had a nice start to his career, the numbers indicate he wasn't really as dominant as O'Flaherty was. Either way, he still had 8 years left in the tank after his age 28 season.
The player formerly known as Fausto Carmona. If picked up anywhere, likely to be on a minor league deal. He had one really good season in 2007 and since then has been a very below average pitcher.
His career is very likely close to being done barring an out of nowhere strong season (he's been below replacement level the last three years and five out of the last six. His most similar player through age 32 is John Thomson who made two starts after age 32 (for the 2007 Royals) before his career came to an end.