If you want off the shelf, TI, nordic, etc chip work fine if you have a decent antenna and transmit with max power you are allowed to in your country. In some countries, like US, you can transmit enough power at 915 MHz to do 3 km if there is not too many obstructions.
If you are more technically adept, or have money for NRE effort, you could use a heavily coded or matched filtered FM signal (i.e. where you transmit 50 bits to send 1 bit of payload, or something like that) that is custom designed for your use.