Linux and Windows binaries are at:
https://sourceforge.net/projects/bitcoin/files/Bitcoin/bitcoin-0.3.20/
Summary of changes and new features (see pull requests for details):
-nolisten : https://github.com/bitcoin/bitcoin/pull/11
-rescan : scan block chain for missing wallet transactions
-printtoconsole : https://github.com/bitcoin/bitcoin/pull/37
RPC gettransaction details : https://github.com/bitcoin/bitcoin/pull/24
listtransactions new features : https://github.com/bitcoin/bitcoin/pull/10
Bug fixes:
New seed nodes : https://github.com/bitcoin/bitcoin/pull/59
New testnet genesis block : https://github.com/bitcoin/bitcoin/pull/53
Optimize database writes : https://github.com/bitcoin/bitcoin/pull/43
-maxconnections= : https://github.com/bitcoin/bitcoin/pull/42
RPC listaccounts minconf : https://github.com/bitcoin/bitcoin/pull/27
RPC move, add time to output : https://github.com/bitcoin/bitcoin/pull/21
several improvements to --help output.