WIRELESS communication

apart from Xigbee ,Bluetooth,WIFI what are the other possible communication between two arduino..???

802.15.4/Zigbee (for example, Xbee Series 1 and Series 2 respectively) Bluetooth Wifi 802.11 RFID/NFC

If you're asking only for wireless comm, the above four pretty much cover the main well-defined wireless specifications that are popular in most sensor applications or manufactured products these days, and certainly those are the most popular ones available to hobbyists, to my knowledge.

However, there are some variants of different frequency-transmission, including basic RF transmitter/receiver pairs; e.g., at Sparkfun, you can search for RF Link Transmitter and RF Link Receiver). I've also seen nRF24L01 modules as well as RFM12B modules used in some Arduino projects.

There are lots of generic wireless modules. The RFM12 is a pretty popular one: http://www.hoperf.com/rf_fsk/fsk/20.htm I think they carry these on sparkfun.com The nordic chips are also somewhat popular. http://www.rfdigital.com/?targetpage=item&filterpn=RFD21733