Do aircraft have radar or other forms of traffic sensing? Quicky question.

Do modern commercial aircraft include radar to detect traffic in their vicinity or perhaps have some mechanism to receive transponder signals.

I know they have forward facing weather radar but the ability to detect and be warned of other traffic on a collision course would seem to be a good idea. 

I'm particularly reminded of the Proteus Airlines Flight 706 incident where a mid-air collision occurred because of visual blind-spots and the ATC not knowing the other aircraft was even out there. I am also aware in this case a transponder monitor would not have helped either...

EDIT:

I suppose TCAS does do the transponder bit, but wont detect aircraft without the necessary device turned on. I'm more thinking of a short range RADAR or even LIDAR, something akin to, though longer range than, the things they are hooking up to cars these days.
By far, most civil aircraft lack radar to display conflicting traffic, and certainly to enhance traffic situational awareness.  TCAS and the use of ADS-B are the most effective tools for traffic conflict and situational awareness information.

Lidar is not presently utilized on civil aircraft for traffic avoidance. 

Keep in mind that TCAS essentially uses the same mechanisms as secondary ATC radar.