I've seen this problem in the past but it had to do with Visual Studio in general. After removing a third party software, in my case: JetBrains ReSharper, intellisense was gone.
In order to make intellisense work again I had to go to:
Tools-> Options -> Text Editor -> C# and make sure that that the "Auto List Members" check box was ticked. Maybe this setting has been unchecked for you?
I'm using Visual Web Developer 2008 and everything have worked fine up til now.
All of the sudden, Intellisense for EPiServer stoped working.
Can anyone help me get this working again?