Exalted has a large amount of supplemental material. If you want to play Solar Exalted using the Core book and you can only afford one supplement, though, get this one.
The Glories to the Most High series has useful setting information and great Charms to expand on what the Core book has to offer. It's easily among the best material written for Exalted's second edition, and I've gotten a lot of use out of it. It's also cheap!
[5 of 5 Stars!]