IntelliSense, plus T-SQL collapse/expand regions.

Want quick information on a column's data type and nullability? Enable the Quick Info feature by selecting Edit > IntelliSense > Quick Info (or Ctrl+K, Ctrl+I). After this, simply mouse over a column in a query for pop-up information, including its nullability and data type.

Have you ever accidentally dropped a production table when you thought you were connected to a test server? When connecting to a new server, click Options and under the Connection Properties tab, select a custom color. Whenever a query window is opened against this server, the status bar at the bottom will display the chosen color (for example, bright red for production!).

Right-clicking a process within the new Activity Monitor allows the process to be tracked in Profiler with an automatic filter applied for the SPID. Further, you can automatically open Activity Monitor on startup of Management Studio by choosing Open Object Explorer and Activity Monitor in the General page of the Tools > Options menu in SQL Server Management Studio.

The missing index DMV information is displayed in the graphical execution plan output. Right-click it and choose Missing Index Details to display the T-SQL to create the index.

T-SQL Debugger (accessed by clicking the green arrow next to the ! Execute icon), with associated Step Into/Over, Breakpoints, Locals, and Call Stacks, is fantastic for tracking variable values as they pass through multiple procedures, triggers, and so forth.

The ability to run a query against multiple servers. Open a query window against a registered servers group. Query results will contain an extra column for the server name.

The Tools > Options menu (SQL Server Object Explorer section) allows you to specify the number of rows for Edit/Select Top N; for example, setting Edit Top <n> Rows Command to 12 will change the right-click menu option for a table to Edit Top 12 Rows.

Powershell integration. For a DBA who is responsible for managing a large number of servers, Powershell is an essential tool. Those who learn it will be one step ahead of most DBAs.

Right-clicking a selection of results in the query output window lets you select Copy with Headers, which allows the results to be pasted into another application with the corresponding column names.