Data Persistence and Remote execution

I'd want to know the possible implementation options .NET provides for the following. The options that I have identified are also given 'neath each requirement.

1. Client Server communication
a) Sockets, b) Remoting, c) Web services

2. Data persistence (preferably in-memory)
a) Remotable Singleton objects (in memory), b) writing to files/database (to disk)

3. Server application triggering off an event in the client
a) Holding client reference in server app thru Call back, b) Remoting of events and delegates, c) MSMQ listeners, d) Server app writing to a file and client implementing a FileSystemWatcher.

If there's anything more you can think of to add to any of the above requirements, do post in.

Thanks in advance,
Jemima.