we're having a project using pic16f877a. we are required to have 2 rf modules communicate with each other using pic16f877a simple tasks as to send a message and display it to a lcd or just simply a 7-segment led. can you suggest a suitable rf module that is already in the market? or can you send me a circuit for this? thank you.

 

There are loads of little PCB or canned modules for this type of thing.

In the past I've used the Radiometrix TX2/RX2 and TX3/RX3, which both work well but need you to do the transmit control and timing in software.

There are also now 'Easy Radio' modules - all you do with these is send a short stream 'message' or 'packet' of serial data. The transmit module buffers it and a few ms after you finish sending, it powers up the actual transmitter, allows the link to settle then sends the data (with error checking) and powers down again.

The receiver stores and checks the message and if no errors, send it out it's serial port..

I'm presently waiting for some of these to arrive to play with; the receivers have turned up but the transmitters are on backorder with my supplier.

Both makers do modules for different frequencies and to suit the regulations in different countries, so check which you can use where you live and you should be able to find a supplier for those.

Edit: Forgot to add the links..
http://www.radiometrix.com/
http://www.lprs.co.uk/