I enjoy the period around the US Civil War, so my favorites are from that period. I really like the Walter Stahr bios. He has a recent one out on Salmon Chase and an older one on Seward, but the one on Stanton is my favorite. I also really liked Allen Guelzo's Redeemer President on Lincoln. I think that's my favorite bio on Lincoln I've read.

Outside of that period I would maybe check out The Fire Is Upon Us by Nick Buccola. It's not quite a biography. It's about the debate between James Baldwin and William F. Buckley at the Cambridge Union. It gets into both people's lives and is very biographical, but it also has a lot of implications for current politics and the beginning of media driven soundbites that really drive the reasoning of the right.