+1 to hefes being pretty quick. See also cream ales and blondes. How long has your other beer been fermenting? If you're over the 6 week mark and you need fermenter space, just bottle your beer and let it age in the bottles.
"Fat, drunk and stupid is no way to go through life, son"
Primary: 90 Shilling
Bottled: Out of beer... need to brew more.
Kegged: STILL out of beer.