Viable plate count
Petroff-Hauser cell count (cytometer)
Coulter Counter - counts cells as they disrupt an electric current flowing across a detector.
Flow Cytometer - counts cells passing across a light detector. Can be used with fluorescent antibodies.
Most Probable Number (MPN) - uses lactose broths. After incubation, a 3-digit number is produced based on the number of positive tubes per set. The number corresponds to a MPN/100 ml of water on a statistical table.
Metabolic activity - using measurements of waste production and nutrient depletion to determine population growth.
Dry weight (biomass) - organisms in broth are dried and their biomass measured.