I read some fairly recent research somewhere where a group of individuals were tested over a period of time (can't remember how long).
Everyone's
vertical jump height was measured to get a baseline.
Group 1 did just squats
Group 2 did just plyometrics
Group 3 combined squats with plyometrics
Group 1's vertical jump increase averaged at about 3cm (just over 1")
Group 2's vertical jump increase averaged at about 3.5 cm (about 1.5")
Group 3's vertical jump increased by a massive 10cm!
So, combine plyometrics with squatting to increase your vertical jump. I believe this is very effective because plyometrics are awesome for improving power, and squatting is awesome for improving strength.
Cheers,
Hav