Who are some underrated players on your favorite team?

Sean Marshall is unbelievable. Leftys can't touch him. Rights struggle with him. He has one of the best 10-6 curves i've ever seen. One of the best, if not the best set up man in baseball this year. Wouldn't be surprised to see him get injured or start to struggle though. He's been over-used the first 1/2 of the season.