After experimenting with the numerous features of SQL Server 2005 in beta 2 and subsequent CTP releases, I have decided upon my favourite features. Although they're not necessarily the most important, they will make my life so much easier.
1. Database Mirroring (High Protection Mode)
2. CLR Hosting (for complex code / calculations)
3. Full Bi-Directional (Peer-to-Peer) Replication
4. Full Text Enhancements
5. SQLCMD (and the dedicated administrator connection)
I should really mention the Service Broker however I haven't (as yet) looked at it in any detail. There is a good resource slowly developing here http://www.sqlservicebroker.com/forums/. There is also a nice tool in dev called the Service Broker Explorer which provides more control over the elements in a GUI. It can be downloaded from here: http://www.sqlservicebroker.com/forums/ShowPost.aspx?PostID=80. I should mention that it is not intended for use on a production system; more of a learning tool.