The clip in extensions became very popular in last one year. It´s simlpe wayto make your hair longer, just clip and go. i had some problems to find good site for buy my hair so there they are!! :P
http://www.foxylocksextensions.com/
http://www.nanicvlasy.sk/
http://vlasky.sk/
http://www.dream-factory.sk/
and many others...