need a GPU for a server

ok so i'm setting up some clients that will be using VM's to run off of..looking for a gpu that doesn't need external power but is still semi decent and not a power hog since the server in which this is all based will be on 24/7..

i have a main rig to game and what not on so for the times where i'm just doing non gaming stuff i picked up some thin clients to minimize power usage. no sense having a rig running with a 980ti and all the other power hungry gear when i'm just browsing the internet.

Do you even need a GPU? Unless you are doing passthrough I don't think one would be necessary and should be able to be taken care of via software rendering.