Pros: passionate staff, great mission, good work/life balance.
Cons: pay isn't amazing, but there are great benefits.
No organization is perfect, but working for the Sierra Club has been a tremendously rewarding experience. The staff culture is amazing; it brings selfless, passionate people together everyday. In addition, you're expected to have a healthy life outside of the office. No one is expected to slave away and work crazy hours.
Overall, I would highly recommend employment at the Club.