Bach Digital is the digital library of Bach's autographs and original parts, the Bach source catalogue and the Bach (and Bach musician family) works catalogue. Whenever possible the information should be accompanied by high-resolution scans of the sources described. You can search by lots of different criteria in this bilingual (German, English) portal.
Bilingual (German, English) database of the works of Bach and their handwritten sources till 1850. You can search by different ways (eg. full text search).
International Music Score Library Project.
The scores of Bach's works are downloadable in alphabetical order / by BWV number.
Bach-Gesamtausgabe ("Bach-Gesellschaft Ausgabe") is also available on this site.
This is a frequently updated website of Bach's cantatas, his other vocal works and many of his instrumental works. It contains texts and translations of vocal works and many other useful informations: discographies, scores, commentaries etc.
This site offers English translations with commentary to the vocal works of Bach.