Network must have plugins

Can someone steer me in the right direction for must have plugins for network plugins.

I also am looking for specific ones as well

1. adding a login bar to the top of all network pages. I cannot seem to find the login button on any network page.

2. centralized log in (if someone registers for one site, they can comment on another board)

3. default settings/forced settings across the network.

4. Recent blogs across the network. I wanna have my main page show recent blogs.

5. Search category across the network.

6. custom registration.

and anything else that can help me out to make the board feel centralized.