Third Millennium Ministries | High-quality, multimedia seminary courses from excellent professors, and all for free! The curriculum is steadily being expanded, so continue to check back.
China Christian Books | This website has a fairly large selection of historic creeds and confessions, along with Christian and Reformed classics.
The Gospel Coalition | TGC is a broadly Reformed network of churches. Among the other offerings on this site is a list of resources, including some in Chinese. Most of these are repeats of those offered at desiringgod.org, but there are a few others as well.
Zanmeishi.com | Extensive website with Chinese worship songs.