Linux and Windows and Mac binaries are available at sourceforge:
http://sourceforge.net/projects/bitcoin/files/Bitcoin/bitcoin-0.4.0/test/
And HTTPS download from the Amazon Cloudfront content distribution network:
https://d24z2fz21y4fag.cloudfront.net/downloads/bitcoin/bitcoin/bitcoin-0.4rc2-win32-setup.exe
https://d24z2fz21y4fag.cloudfront.net/downloads/bitcoin/bitcoin/bitcoin-0.4rc2-win32.zip
https://d24z2fz21y4fag.cloudfront.net/downloads/bitcoin/bitcoin/bitcoin-0.4rc2-macosx.dmg
https://d24z2fz21y4fag.cloudfront.net/downloads/bitcoin/bitcoin/bitcoin-0.4rc2-linux.tar.gz
The d24z.... downloads are an experiment; I like that they're https, I don't like the obscure d24z... URL (that's actually github's CloudFront id; I asked, and they have no objections to linking directly to the https version of the downloads).
Executive summary release notes:
The main feature in this release is wallet private key encryption;
you can set a passphrase that must be entered before sending coins.
See below for more information; if you decide to encrypt your wallet,
WRITE DOWN YOUR PASSPHRASE AND PUT IT IN A SECURE LOCATION. If you
forget or lose your wallet passphrase, you lose your bitcoins.
Previous versions of bitcoin are unable to read encrypted wallets,
and will crash on startup if the wallet is encrypted.
Also note: bitcoin version 0.4 uses a newer version of Berkeley DB
(bdb version 4.8) than previous versions (bdb 4.7). If you upgrade
to version 0.4 and then revert back to an earlier version of bitcoin
the it may be unable to start because bdb 4.7 cannot read bdb 4.8
"log" files.