As Terran
Make:
RavenScan
MarineDetection and split movement remove most of the mine threat.
Open in the counter tool with Widow Mine tagged ->As Protoss
Make:
Observer
Stalker
DisruptorObserver coverage matters more than adding one perfect unit.
Open in the counter tool with Widow Mine tagged ->As Zerg
Make:
Overseer
Zergling
HydraliskTrigger mines with small groups before the main army arrives.
Open in the counter tool with Widow Mine tagged ->
Marauder
Reaper
Hellion
Hellbat
Cyclone
Siege Tank
Thor
Viking
Medivac