The real boom in PTC industry started with two major players, Adbux and Bux.to, although a few were known to exist that never attracted much attention. These two websites drew huge amounts of visitors with their powerful advertising campaigns. At one time, Bux.to ranked at the 300th position on Alexa.
Lately a number of PTCs have started blooming, most of these lasting a few months at the most. This is due to the fact that the sustainability of the PTC business model is questionable, and scamming webmasters have made the situation worse. It is not uncommon to see a PTC website disappear overnight. Some websites maintain a list of PTC Scams [1] to alert newcomers. Others feature PTC Reviews [2] and Forums [3] where users can discuss about PTCs.
A new generation of PTCs has started emerging lately like NeoBux which continually keep revising and tweaking themselves to evolve an efficient survival strategy. Some of these websites offer instant payouts, wherein the website's script credits the user's account as soon as he cashes out. These websites also feature fraud prevention and hacker-proof technologies.
one of the best sites i have seen is http://www.incentria.com