Recently my intellisense on Visual Studio 2008 stops working, after some search I found a solution at
http://blogs.blackmarble.co.uk/blogs/rfennell/archive/2007/12/01/intellisense-not-working-in-visual-studio-2008.aspx
I had a poke about in Tools|Option and found that on the Text Editor|All Languages that the three checkboxes for Statement Completion where showing neither empty or checked but a fully coloured box - which usually means an unknown settings. So a set these all to checked (a tick) and my Intellisense started working.
This saves me a reinstall of Visual Studio.