As at June 2011 the recommended way to install nVidia drivers in Debian is to use the packages nvidia-glx + nvidia-kernel-dkms. The dkms package is triggered automagically every time linux headers are installed - and makes sure the kernel module is up to date (I don't really understand this in greater detail, because it works fine :)
So to make sure the drivers are installed with the current and future kernels you have to:
aptitude install linux-headers-2.6-686-pae nvidia-glx nvidia-kernel-dkms
where linux-headers-2.6-686-pae package will pull the latest headers, when a new kernel is installed.
