Changes:
- Fixed a wallet.dat compatibility problem if you downgraded from 0.3.17 and then upgraded again
- IsStandard() check to only include known transaction types in blocks
- Jgarzik's optimisation to speed up the initial block download a little

The main addition in this release is the Accounts-Based JSON-RPC commands that Gavin's been working on (more details at http://bitcointalk.org/index.php?topic=1886.0).  
- getaccountaddress
- sendfrom
- move
- getbalance
- listtransactions

Download:
http://sourceforge.net/projects/bitcoin/files/Bitcoin/bitcoin-0.3.18/