What is the GPU driver I am currently running?

Update typing:

nvidia-smi

gives you the driver verson nowadays.

Old answer:

Typing nvidia-settings --version will tell you what version of the NVidia driver is currently installed (even when it's not running).

lsmod | grep video will show you the running video module.

modinfo szWhateverWasTheOutputOfThePreviousCommand will give you the version of the running module.