PTC means Paid-to-click, where sites pay you to visit sites for a period of time (usually 30 seconds). They're all free to join, and require no skill to make money. Most of them are international-friendly, too. I like these sites a lot because you can visit multiple sites and have them open at the same time, allowing you to make money as quick as you can click on the banners. All of the sites I have listed allow you to use either Alertpay or Paypal. If you haven't gotten an account with those two, you should do so now. Register with Alertpay or Paypal.
There are two types of paid to click sites, the sites where you make your money solely based on your own clicks (like Clixsense) and the sites where you make your money through referrals (like Neobux). Referral sites are much more profitable, but sometimes require you to invest time and money.
Sites that you earn from referrals
The key to making a lot of money with these sites is to gain referrals. The more referrals you have under you, the more money that you make when they click on ads. These sites allow you to buy or rent people who have joined the site unreferred, but you can also refer people using your referral link. The free accounts allow you to click on a certain number of ads a day, but if you want to pay a yearly fee they will give you more ads to click and more money per click. Paying this fee isn't necessary though, you can still make plenty of money using a free account.
Generally I do not condone spending money on anything online, but there are certain companies that you must spend money to get money. With these sites, you have to look at the money you put into them as an investment. If you manage your referrals well, click your ads every day, and use a good strategy...you can get back your investment within a short amount of time. You HAVE to visit the forums and read all the rules, tips and strategies to make the most of your investment.
Specifically with Neobux, if you invest in a gold membership and rent 400 referrals you will gain back your investment very quickly. With BuxP, you are better off trying to gain direct referrals.
Sites that you earn only from your own clicks
I would suggest that you join as many of these sites to click sites as possible, because each of these sites give a limited amount of banners to click a day. The more sites you have, the more ads that you can have open at one time, and the more money you make. Generally, these sites offer you $0.01 per ad that you click. One of the main keys to these sites is that you have to check them several times a day, because new ads are always popping up.
On my Paid to Click Sites page, I've listed the best, most reliable, paying PTC sites that I've found so far.