Aug. 18, 2008: The domain name bitcoin.org is registered. Today, at least, this domain is "WhoisGuard Protected," meaning the identity of the person who registered it is not public information.
Oct. 31, 2008: Someone using the name Satoshi Nakamoto makes an announcement on The Cryptography Mailing list at metzdowd.com: "I've been working on a new electronic cash system that's fully peer-to-peer, with no trusted third party. The paper is available at http://www.bitcoin.org/bitcoin.pdf." This link leads to the now-famous whitepaper published on bitcoin.org entitled "Bitcoin: A Peer-to-Peer Electronic Cash System." This paper would become the Magna Carta for how Bitcoin operates today.
Jan. 3, 2009: The first Bitcoin block is mined, Block 0. This is also known as the "genesis block" and contains the text: "The Times 03/Jan/2009 Chancellor on brink of second bailout for banks," perhaps as proof that the block was mined on or after that date, and perhaps also as relevant political commentary.
Jan. 8, 2009: The first version of the Bitcoin software is announced on The Cryptography Mailing list.
Jan. 9, 2009: Block 1 is mined, and Bitcoin mining commences in earnest.