the best plugin in this range available for (in) Cubase is:
External plugin and route the signal to the real tubes
Sorry, I just had to...
But I know Antares have plugin that emulates tubes.
Nomad Factory have more of this stuff in their bundles and also they have Tube Levelling Amplifier which emulates a Fairchild (I guess) as a stand alone.
Than there is a tritone digital:
http://www.tritonedigital.com/with not only Colortone...
Also:
http://www.camelaudio.com/camelphat.phpDon´t ask me for quality, as I do not use them-I use real tubes when I need this kind of warmth (but Colortone has pretty good rewiews). The best way is to download the demos and compare which one you like ....
And maybe you should consider this also:
Waves SSL Bundle
URS classic console compressors and EQs
PSP Vintage Warmer (emulates tape saturation)
I use theese often in my DAW. But I have to say I use their AU versions, not VST.
Good luck!