Vindale Research

Star Rating:
Initial Investment: $0
Optional or Maximum Investment: Trial offers can cost anything from $10-$100 but you will get reimbursed... mostly.
Other Names: ----
Amount of signups, spam and suspicious links: As much spam as most survey/trial sites. Fairly tame with suspicious links.
Cash Out Level: $50
Review: Although this site promises up to $75 for surveys, it's not the surveys they are paying you for. Instead they ask you to sign up for trial offers that can cost you quite a few dollars and then pay you enough to cover the trial offer and a little bit extra. So if you spend $40 on a trial offer they might pay you $50, meaning you only made $10. So yes, you can earn but you need to make sure you don't remained signed up for trials as this may leave you out of pocket quite a bit - and your earnings will realistically be a lot lower than promised. How can they call it a survey site? They simply send the same basic survey at the end of each trial offer.

People String

Star Rating:
Initial Investment: $0
Optional or Maximum Investment: $0
Other Names: People Stream
Amount of signups, spam and suspicious links: 20%
Review: You need to receive a mailed card which takes thirty days before you can start earning - and many people have problems getting this at all. Many people have reported deleted accounts and referrals not showing. And it's almost impossible to get an answer from the site admins. And all that is BEFORE you even get to the part where you're earning the pittance they promise. Oh and did we mention that people outside the US/Canada often don't get paid at all? So sure, if you can get through all that, good luck with the earning!

Dubli

Initial Investment: $700+
Optional or Maximum Investment: $5000+
Other Names: Goobli
Amount of signups, spam and suspicious links: 5%
Cash Out Level: Usually people buy items, they don't cash out.
Review: Tokens are purchased at 80c and each token can lower the price of an item in their reverse bid by 20-25c. So already they're making 55c. Despite claims of people buying $200 items for $50, those items are few and far between, and are highly bid on. It's complicated to explain, but if you dig deep, you'll find that they have a great "storefront" but when it gets down to real item buying they end up taking a lot of the money and you can easily lose out.

Pure Profile

Star Rating:
Initial Investment: $0
Optional or Maximum Investment: $0
Other Names: -----
Amount of signups, spam and suspicious links: 5%
Cash out Level: $25
Review: This site is a genuine survey and ad click site. You simply click the "Go" button on the main page and do each activity as it appears. Some require a simple ad click, or a five to twenty minute survey, and occasionally a signup. Each offer pays from 10 cents through to $5 or more. Although they send occasional emails letting you know that you have new offers, the best way to earn is to login every few hours and check for new offers - on average you'll get about 10-20 a day depending.

Rewards Central

Star Rating: 
Initial Investment: $0
Optional or Maximum Investment: $66
Other Names: Email cash, My opinions.
Amount of signups, spam and suspicious links: 5%
Cash Out Level: $33
Review: This site operates in Australia and the UK and is one of the few that will never require you to pay to earn - even for trial offers. They split into two sites several years ago (My Opinions and Rewards Central) but each can be used to transfer cash back and forth. You get a few free SMS daily, free daily guess games, free daily clicks and a fairly good number of surveys which can pay up to $10 each. If you're into shopping online you'll earn even more - if you click their link before purchasing through eBay, you can earn points, along with many other internet sites. So why not get money back on what you're already purchasing online? They even have a banking system where you can earn interest on your current points. Overall, one of those sites worth a five minute visit each day to see some nice rewards. Their gold membership is completely optional and isn't required to access anything important other than gold level auctions and a higher interest rate in the bank, plus a few special offers from online shops.