I recently signed up to for some paid market research and was invited to take part in an international postal survey. All I do is receive and post a few test items a week and log these online. Really simple, they supply everything I need. I’ve just completed my 1 month trial and received my first reward! 
Looks like they’re still recruiting so you can apply via the link below if you are interested? I would definitely recommend!
survey.tns-online.com/
Are there any other good surveys you heard of or tried yourself?
Let's share our experience here! The more, the merrier 