Security for the infrastructure room.. (I don't care if it's a closet or a multimillion dollar server room..) Solid core, fire rated doors with appropriate locks. (Amazing how many businesses don't have the minimum there!)
As someone else said, conduit and wiring ability to expand over time. If someone wants to run 1" conduit, double it to 2" or 3". In the future there will be some new technology and it's almost impossible to ever remove old wiring, but adding new will be much easier.
Climate control -- note I didn't say air conditioning. For the best results, the room should have the ability to have it's own climate control. This may mean air cleaners (if fresh air is used for heating/cooling), air conditioning unit, etc. Don't rely on the building system, because as technology changes the heating/cooling requirements of the technology will change.
A space twice the size you need.. Equipment is always changing in size.. both bigger and smaller, as are the company needs.. room to grow is a good thing!
Finally power.. the room should have it's own dedicated power feed, that can easily be managed by a generator, power backup unit, etc.. even if you don't need those things today, planning ahead for them makes it a whole lot cheaper if you do ever need them. Again relying on building wide power is fine for a while.. but it's much better to have the ability for dedicated stuff in the IT room.