Guitar rig is excellent, but if you couldn't afford to buy a regular amp, you most likely won't be able to afford that either!!
You might be good just using free trials of the above mentioned programs until you have the money saved to get a real amp.
The software I would suggest is called Amplitube. It is made by a company called IK Multimedia. They have a plugin version to interface with VST, RAS, all those formats, as well as a stand-alone version that works quite well (called Amplitube Live if I remember correctly).
I have tried guitar softwares but there is always audio latency involved. Is that the case with everyone?
Is there any better software with distortion and zero latency?
Besides latency I believe that guitar softwares are very good for producing various effects like wah wah and reverb.