Road bike tyre size for a mountain bike
I think what you are looking for are a pair of "slicks" for your mountain bike.  They come in a number of sizes for 26" wheels.  Batman suggests looking for a set between 1.7 - 1.9"  That is a good suggestion since you will be able to use the same tubes are are in your 1.95 mtb tires.

If you are willing to get a new set of tubes with those tires, I would suggest looking for 26 x 1.25 - 1.5" slicks.  It is a matter of preference, but I find them to be a bit quicker and responsive if you are willing to run the associated higher pressure.  If you commute has lots of curb jumping, pot holes, or broke pavement 1.75s may be my choice... 

My experience is that 1.95 slicks really dont offer much over a fast rolling knobby tire.