Referrals are by far the best leads available to a real estate agent!
A few words of caution though...
You better bring your "A" game, because if you don't, those referrals will come back and bite you in the behind!
Unfortunately, I see this quite often. A referral is derived from a former satisfied client. These referrals are seen by quite a few agents I know as money in the bank. Therefore they squander the opportunity by not performing at the level of service that earned them the referral. Not only does this leave the new client unsatisfied, but the former becomes a non-referrer as a result.