His overall numbers don't look that great (2-2, 4.43), but Jeremy Bonderman has been great in May (1-1, 1.80). Although he's been in the league since 2003, and has plenty of talent, he's only had one truly great month in his career: June 2006 (2-0, 1.77).
His great pitching in May is a surprise, not only because of his miersable April (1-1, 6.97), but because he was coming back from multiple serious injuries over the past few years (blood clot, pain in right shoulder).
Among 60 AL pitchers with at least 20 IP in May, he has the 2nd best ERA (behind Justin Verlander). Not only does he have a great ERA, he hasn't allowed a HR, and has 20 SO with only 5 BB. It's been a long time, but he was emerging as a real force after the 2006 season, despite finishing with an ERA of 4.08.
He pitched very well in the postseason that year, including a dominating performance against the Yankees in the ALDS. He only pitched 80 innings over the past 2 years because of injuries and is only 27, so he could have a lot of productive years if he can stay healthy.
He doesn't have a great track record for consistency, but this might finally be his year. His teammate Joel Zumaya is also having his best season since 2006 after several injury-marred seasons. It's only been a few starts, but he has a great chance to get his career back on track, and have his best season yet.
Update: Last night (May 26th), Bonderman was terrific against the Mariners (7 IP, 5 H, 0 ER, 2 BB, 6 SO), but the bullpen didn't hold it and the Tigers lost. His May ERA is now 1.33, which is the best in the AL in May among all starters.