What 64bit machine should I get?

I need to purchase or lease some 64bit laptops very soon.  I'd love to hear your opinions on what to get.  They will be used initially for virtualization, high performance and compute cluster testing.  However, I'd like to leverage the knowledge around the machines for the next platform refresh for my team.  With that in mind, I'd like to know if you encountered driver and application issues running IE, Office, Virtual Server, etc.

So what would you buy and recommend?