Patton is a good example, and one (IMO) well worth reading up on. Nelson Miles is a good example of a good leader (initially) who was eventually overcome by his own weaknesses. Spruance repays study, as does Ernie King (volcanic temper and all). I'm not a huge fan of Eisenhower, although he's an interesting study in the political aspects of leadership and command. Grant is a good study as well. As for more modern leaders, Mattis is worth a long look.

I'm sure others here will have ideas and suggestions as well. Many of the leaders I study come from the Frontier Army, which is a pretty specialized (and obscure) field.