I've done usertesting.com before, and only gotten paid once! I almost never qualify for any of the surveys.
I dogsit/walk dogs on the side. It's amazing how quickly the money adds up, especially in my town where everyone has dogs. I use Rover.com for some of it, which is nice because they find people for you, and give you the options to say yes/no. I also just tell everyone I know that I dog sit, so I get a lot of business just from friends/connections. I could probably have dogs every day of the month if I wanted, and make about $1000-$1500 extra a month. I usually just do it 2-3 times a month though, because I value what little free time I have after working 50 hours a week at my normal job. Still, in a good month of 2 long stays I'll have about $300-$400 extra which is nice.