The two great sounding Kuassa Rack Extensions Vermilion and Creme (guitar amp simulators) are updated today for additional oversampling options. Oversampling techniques were added to prevent aliasing. This can become a problem when you saturate a signal that will create overtones which, when they are higher than half of the sampling rate (in case of 44.1: above 20 kHz), are nasty and non harmonic.
I have tested both Rack Extensions and the 8 times oversampling setting is really smooth. Choose a lower setting if CPU usage is an issue (you might leave it at its default setting and only change it when mixing or making a bounce).
The Blamsoft DC-9 Overdrive is another mighty fine sounding Rack Extension for guitar players that uses oversampling options which can be found on the back of the device. Clever and convenient.
P.S. It seems that these oversampling options are only available for the RE versions of these lovely virtual amps. Great news, guitar players using Reason have all the luck!