The most trusted site out there, and the highest ranking by terms of annual traffic, www.NeoBux.com is the safest, and fastest paying, they have a very unique system that you have to check out and read for yourself, the way its set up how you can rent referrals who you automatically earn off of, its the perfect no investment plan, on the forums, in the success stories section, theres actually one couple whos 08 earnings was 0$ to 89,000$ combined, mind you after they had started to rake in money, they invested some of their own money, but the idea is to think small, and in time you will click enough money on your own to start renting referrals, they cost 25 cents each, and you get them for 30 days, so if they are active, you earn, there is some math involved if you want to see large profit, you will eventually have to have a daily income report, if you want to profit, you need a average of more than 1.00 of course. then you work from there, but check it out.
Heres some sites that I use AFTER I've done all my work on neobux :P its an addicting site, the community is huge and fun :P
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LinkGrand :
This site is my second site based on rank. Has very low payout, and a unique referral system. Very busy on the weekends. Pays with PayPal.

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WordLinx:
This is #3, another good site, with very good referral system. High pay per click %, but only 5-6 ads a day maybe.

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Hits4PayI like this one, when you sign up, they basically give you a email inbox, and you get "emails" daily which you click, pays very very well, but pays by cheque. HAS A 10$ Bonus sign up going on u, so you have to check it out.
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You-CubezYouCubez has to be the most unique, in terms of style really, its a really fun concept that instead of clicking ad links or banners, you click a colourful cube! This is the highest paying pay per click site I have, because it pays in british pounds, not american dollars, so ofcourse the exchange rate is phenominal for us :)
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BombLogic:
Bomb logic is a slow one, its mainly geo-targeted, so since im in canada I only get maybe a few clicks a day at most, all depends where you live, still trusted though.