By default Visual Studio 2010 comes with Intellisense feature enabled. By the way, there are some cases that it’s disabled – can be caused by anything (setting changes on add-in installation, importing settings, human error, your teammate :), etc).
The fix is simple, just open the Tools -> Options, then go to the Text Editor section. Select All Languages or specific language (in this example C#).
Then make sure Auto list members and Parameters information are checked. Click OK and it should be working now.