My Review
Revtwt is the preferred method to make money with Twitter by many people. They are unobtrusive and have many ads to post as well as a Shorten url service which you can make money with and also a nice referral program. I have not reached payout with them yet as I just started using my twitter about 2 weeks ago and only learned about them a week ago. I have looked at reviews and they seem to be pretty good. It helps a lot to have a good bit of followers because that gives more people who may click on the ads.

Allowed Countries
Seems to be allowed everywhere.

What They Are
You enjoy tweeting with your friends, but wouldn't it be great to make a little extra cash on the side while you post on Twitter? RevTwt has the solution: we give you links to post on your Twitter account, and you earn money each time someone clicks on your link!

How Much Can You Make
It depends on your amount of followers and how many will click on a link that you post!
Each CPC ad is different, currently ranging from $0.04 to $0.20 per valid click. Please note that only valid clicks are paid and all clicks are audited.
A valid click is a click by a real person clicking on an ad out of genuine interest and free will, and is physically in a country targeted by the ad. Clicks that are suspicious of click fraud will result in an account being red flagged or banned permanently.

Form of Payment
You can withdraw your earnings to your Paypal account once your earnings exceeed $20. If you submit your Paypal withdraw request before 5:00pm on Monday, your payment will be processed on Friday of the same week. If your Paypal withdraw request is made after 5:00pm on Monday, it will be processed on Friday of the following week.
 
If you can't get a Paypal account, you can request payment by check. Your earnings must exceed $100 to request a payment by check. Check payment requires up to 15 days to process.

Referral System
The RevTwt referral program is a great way to spread the word of this great service and to earn even more money with your Twitter account! Refer friends and receive 20% of their earnings for life! Just send them the link below, post it on your Twitter, post it on your website, or any other way without spamming

Upgrading
Elite Twitterers Program: Earn at least twice as much from Elite Ads.
How to become an Elite: No spamming (ads not more than 20% of your tweets), No click fraud and more than 8,000 followers.

IMreportcard's Reputation Review
RevTwt seems is getting good feedback from the people who’ve used it. Of course, those with the most followers on Twitter are going to see the best results. Reports from members of this program are that they do pay, and in a timely manner. That’s an important thing. If you have a good Twitter following, this program might be worth looking into.