Ishita
One of the best ways to get people into organizations has been thru referrals, traditional yet effective. What you do is, tap into a vast network of passive/active candidates thru your existing employees who spread the word out to their friend and ex-coworkers. The foundation of the referral scheme is "trust", because we trust our friends/colleagues we are more keen to listen and try the opportunity they present us.
There is surely a carrot as well, each successful referral is rewarded with either a cash bonus or in kinds ( gift certificates ) to the refer.
Referral schemes (RS) should have clarity on the objective and possible conflict situations ( like in cases you see same resume's from two/three different sources ). Mostly the referral bonuses are paid out in parts, (eg::30 % at the time of the candidate joining and 70% in six months/9 months ..etc ). This in a way also ensures that the refer will make sure the referee continues employment, although there are no guarantees.
RS is a internal sources of recruitment, other internal sources is also existing pool of resources within the company, internal ads can tap into that pool.
External sources are online job boards, staffing firms, news paper ads etc.