How to get the nvidia driver version from the command line?

Using nvidia-smi should tell you that:

bwood@mybox:~$ nvidia-smi 
Mon Oct 29 12:30:02 2012       
+------------------------------------------------------+                       
| NVIDIA-SMI 3.295.41   Driver Version: 295.41         |                       
|-------------------------------+----------------------+----------------------+
| Nb.  Name                     | Bus Id        Disp.  | Volatile ECC SB / DB |
| Fan   Temp   Power Usage /Cap | Memory Usage         | GPU Util. Compute M. |
|===============================+======================+======================|
| 0.  GeForce GTX 580           | 0000:25:00.0  N/A    |       N/A        N/A |
|  54%   70 C  N/A   N/A /  N/A |  25%  383MB / 1535MB |  N/A      Default    |
|-------------------------------+----------------------+----------------------|
| Compute processes:                                               GPU Memory |
|  GPU  PID     Process name                                       Usage      |
|=============================================================================|
|  0.           Not Supported                                                 |
+-----------------------------------------------------------------------------+

On any linux system with the NVIDIA driver installed and loaded into the kernel, you can execute:

cat /proc/driver/nvidia/version

to get the version of the currently loaded NVIDIA kernel module, for example:

$ cat /proc/driver/nvidia/version 
NVRM version: NVIDIA UNIX x86_64 Kernel Module  304.54  Sat Sep 29 00:05:49 PDT 2012
GCC version:  gcc version 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5)