I actually wrote this up as an e-mail for someone, but think sharing it here will also prove useful for folks.
This is the modern Chinese -> English dictionary. I use this one a lot.
Classical Chinese and character dictionary (simplified):
This one has the Foguangshan Encyclopaedia as well as a few others (some English). The Chinese->Sanskrit dictionary is also highly useful.
This is another site by DDM that is extremely useful. It is a database of names complete with birth and death dates (or reliable educated guesses):
The MW Sanskrit dictionary is useful, too, but the input romanization is tricky (it uses Harvard-Kyoto, which Wikipedia can provide info for):
Another older Chinese Buddhist dictionary:
For Classical Chinese this site is also useful.
It doesn't have anything to do with Buddhism, but has the whole classical canon online with many texts having running English translations alongside. The dictionary is useful to some degree, too, as it gives simple definitions as well as examples in usage across the canon. Almost all pre-Buddhist, but in some cases necessary (especially when a native Chinese author is using terms derived from the Analects of Confucius or some other canonical text which almost all Chinese authors in pre-modern times were educated in).
The whole Taisho, unlike CBETA which excludes all Japanese authors (though they wrote in Chinese)， is available here (though the interface is awkward):
Actually when reading texts having commentaries by Nara period Japanese monks on hand is useful as they define terms and interpret nebulous passages.
Finally, this isn't a dictionary, but Asia Major has all their articles two years and older available online as pdfs (right now everything up to 2009 is available). A lot of good articles on Buddhism in China: