There are hundreds of companies for you to chose from. The only way to really find out which ones pay well is to work for them and compare their pay to other companies. There is one company, Corporate Research International, which has hundreds of jobs, but the pay is very low. For example, they require you to shop 5 departments at Lowe's and the pay is only $5.00 plus a $1.00 reimbursement. I haven't found another company that pays as little as they do. You really should go to Volition.com or Walletboosters.com and sign up with a few companies whenever you have time. The jobs will start to pour in and you can evaluate the pay when you receive e-mails from all these companies.
Here are a few names I know of that are nationwide: Shop'NChek, Bare International, Corporate Research Solutions, Consumer Research Group, EPMS, Trend Source.
Good luck.