Depending on which brand, but according to Nvidias website the 750 Ti can support up to 4 Displays. but the EVGA 750 Ti can only support up to 3 monitors 1x HDMI 1x Displayport 1x DVI. While the gigabyte version of the 750 Ti can do 2xDVI 1x HDMI 1x Displayport.
also you can always run another monitor Via your CPU iGPU, many motherboards have the option to enable iGPU Multimonitor from the bios.
I am currently running 2 monitors of my GPU HDMI+DVI then another HDMI from the Motherboard via iGPU.