The IACR eprint archive, which is essentially arXiv for cryptography. Essentially everything worth reading in cryptography is either in the IACR eprint archive or a conference proceeding. All conference proceedings from the IACR conferences can be read online for a fairly cheap membership fee. More often than not everything is cross-posted to the eprint archive even if it's published in a journal (which there's basically one: The Journal of Cryptology) or a conference.