There are a number of “form filling jobs" available online, from buy-in services to free survey banks, there are many variations. The list below is rated from lowest rating to highest. I've personally used every variation listed below, along with about 15 others.
Getting Paid per Offline Form
You can buy in to one of these offline form services where they mail forms to you, which you fill out, then send back. They pay well but the downside is, they usually require you to pay a monthly fee and a start up fee. I don't recommend this for new comers, make sure your ready for this if you decide to enroll in a program like this.
Getting Paid per Online Form (directly through merchant)
Every once in a while you'll find a merchant offering paid surveys directly. Take advantage of these when you find them, they are rare and difficult to find. Usually you have to make an account with there website first though.
Getting Paid Per Online Form through a Form Job Bank (HIGHLY RECOMMENDED):
If you're serious about filling out forms for money, and you're new to this area, I strongly advise you to start here. They are free to join, no credit card required, and no fee's ever. All surveys are free. These survey banks buy the surveys from other merchants online, and take a small percent of the profits when you complete the survey. For example, if NetFlix is paying 20$ per survey, the form bank will pocket 1$ and give 19$ to you.
If your new to this area, I'd advise you to start your form filling career using a Form Job Bank. If you're experienced, you may want to consider getting into the offline forms.
I've tested hundreds of form filling services, this one is a free form filling job that doesn't require a credit card, and has the highest pay outs.