Purchase RF module!!!

hi! i wanna create a wireless sensor network which needs a RF Transceiver.i searched some circuits and build them but they couldn't work properly due to some inductor and antenna designing problems.now i want a ready-made RF transceiver which is capable of sending and receiving the serial data,for my senser nodes and base station.
can anyone help me in this regard to purchase an RF module(Ism Band)?i need a guidance about genuine companys...do any company send me a free sample of RF module?

The frequency depends on what can be used in your country. Ask the authority that regulates radio in your country or read their website.

433MHz can be used without a license in many countrys.

Companys that sell off the shelf modules include
LPRS
RF solutions
Telecontrolli
Radiometrix

Check this,..