Sudipa,
As someone rightly mentioned,job portals, employee referrals, campus recruitments are the various tools which we use depending upon the requirement. Out of these employee referal and campus recruitment are the most cost effective (neglegible cost) followed by the portals where you have an option of subscribing to the different available packages for getting access to the CVs available in the portal ( Naukri is generally preferable). In case of critical profiles you can always take the services of Recruitment consultants.
On this site you can find various articles which shows ways and means to foster employee referralm system in your company.
All the Best and Happy Recruiting
Amit