I have tried to separate the PTR (Paid to Read) sites from the PTC (Paid to Click) sites, though there is often some crossover between the two types. These are generally the easiest to earn money on - in the case of PTR sites, they usually offer paid e-mails, which you can either have sent to your preferred e-mail address or read on site (or both), as well as on many you can also click ads, usually for up to $0.01 per ad or less, much like the PTC sites. Many also offer other ways to earn cash and, like PTCs, many offer great benefits for bringing on referrals.
Most pay you a percentage for your referrals' paid e-mails and clicks as well. In some cases, if you upgrade, you can earn more both for your clicks and paid mails and your referrals' clicks and mails.
You can usually cashout with a PTC or PTR anytime you have reached the required minimum cashout level; any variations to this will be noted below. Some will have a longer wait for payment for free members (usually 28-30 days) than upgraded members.
I would recommend setting up a separate e-mail address (Gmail is preferred by most sites) for your PTR/PTC activities especially, as well as your GPT activities if you do GPT. Some only offer payment by PayPal and/or check, but you may also want to consider setting up a Payza (formerly AlertPay) account rather than using PayPal to get paid by many of these sites that offer alternatives to PayPal, due to PayPal's restrictions on PTC activities (although many of these sites also offer payment by check or otherwise).