Wordlinx is another good and established program I joined last week. They have been in business for over than 4 years and have almost 57000 members.
They have also a different approach on PTC, as you can directly use what you've earned through your cliks to buy visitors for your own advertisement campain.

Make sure you join their mailing list as they'll pay you upto 5 cents just to read their update mails, and you can also earn from $0.01 to $0.05 for emails sent by advertisers through that mailing list.

Membership :

$0.01 per link clicked (as a free member you'll receive around 4-5 links daily, sometimes more, sometimes less)

$0.005 per referral click

Minimum payout is $10 through Paypal

You an buy referrals at $1 each, but they don't always have available referrals to buy, however, when all are sold out, they do give a date when you'll be able to buy .

They have 3 different upgrades :

Verified Membership $5 per year :Verified Buyer Status Tells advertisers you can buy online, and your own ads are targeted at other verified buyers
100 Visitors will be Added To Your Account Advertising sample, worth $2.10 (once)

Premier membership $10 per month : you will have the verified status +

Unique Visitor Targeting (Each member can only click your link once)

Visitor Location Targeting (Target regions like America, UK and Europe)

Half Price Visitor Fees (5% + $0.50) >>Pay less when buying visitors

Pro membership $25 per month :Same features as Premier membership +
Half Price Visitor Fees (5% + $0.50) >Pay less when buying visitors

Half Price Banner Ads (just $25 p/m!) >Pay less when buying banner advertising

Half Cashout Level (just $5 instead of $10)

2 x Affiliate Earnings (10% per sale) >Earn double when your referrals buy visitors

2 x Referral Earnings (10% per click)

2 x Referral Bonuses ($0.10 each) >Referral must click an advert to qualify

2 x Upgrade Bonuses ($2.00 each!)> Referral must upgrade to qualify

3 x Bonus Earnings ($0.45 per $10!) >Earn triple bonuses when browsing ads

1000 Visitors Added To Your Account

100 Visitors Per Active Referral (Referral must click 50 adverts to qualify)

Advertising :

Wordlinx has different means of advertising, at rates beginning at $6.50 for a full campain (to the whole member base)

You can also advertise to the 4500 confirmed e-mail subscribers and the price begins at $59 (for $0.01 mails) up to $249 (for $0.05 mails). These will be unique visitors, as only one e-mail will be sent to each subscriber.

Obviously you can also choose banner advertising. For $50 per month., your banner will be displayed at the "browse ads" page and will be seen by all the members.

My opinion

As of today, I'm fully satisfied with this program, I'm not upgraded and have no referrals, and I did earn around 40 cents in a week or so, which is a very honnest rate.
I foresee to upgrade as verified as soon as I can, in order to receive more ads daily.
I'm confident about this site, as it's in the business since more than 4 years, and are also sustainable.