Where can I find a roadmap of the main bitcoin client? Wallet encryption is long overdue, and AFAIK is coming in the next client version (0.4.0). What are the next planned milestones in the development of the main client and/or protocol? Where can I find information about that?
You can read the Roadmap and the status before v0.4 release

They discuss the development at
http://sourceforge.net/mailarchive/forum.php?forum_name=bitcoin-development