The VirtualWire is for the cheap on/off RF modules.
The VirtualWire makes the protocol in software.
Switching the transmitter on and off is called ASK.http://en.wikipedia.org/wiki/Amplitude-shift_keying
Typical hardware chips for a protocol are the CC1101 modules.
The 1 km modules use FSK.http://en.wikipedia.org/wiki/Frequency-shift_keying
I can't tell if they have a chip for the protocol or not (I think not). There is not enough information on that page.
There are other 433MHz modules like that. But I would not rely on them to get as far as 1km.
You could use a module like that, but with an antenna connector and use directional antennas.
And some modules have LNA. Search Ebay for "cc1101 lna" and you will find some.