I think this one is going to do well
http://www.neobuxreferrals.org/index.phpThe co-op is cheap and the site is easy to join.
You can put your referral link in free or for between
$3 - $5 per month you can buy into the co-op. I am
trying the $5 one month option and I have 900 hits,
no signups in two days.
If it can continue to produce that much traffic, then
it only has to deliver a few active referrals per month
in order to give a positive return on investment. It is
thus a no brainer.
I'll let you know if it generates any referrals for me