Only known reputable survey sites are listed here. These sites pay users to participate in market and academic research of various types.
FocusGroup / Sago : Owned by the same company and connected by a single login, FocusGroup focuses on standard market research surveys while Sago offers better-paying in-depth product tests and longer personal interviews.
Paidviewpoint : One of the oldest market research survey sites, specializes in shorter and simpler surveys for web browsers. Referrals can earn a percentage of their signups first cashout (when they complete at least several surveys).
SurveySavvy : Another long-running survey site that has a mix of long and short surveys for brands doing market research, with occasional product tests. Incentives come from "trees" of both direct and indirect referrals.
Tellwut : Brand and retailer surveys, affiliates can have unlimited signups but are limited to roughly $1 in value per signup (once they complete at least one survey).
Toloka.ai : A more "entry-level" AI training tasking site that takes just about anyone but gears its pay more toward workers in developing countries.
YouGov : A leading survey site often cited in political polls, specializes in both those and research for big brands. Anyone can sign up to take surveys for pay. Referrals earn "points" that accrue and can be cashed out for a wide assortment of gift cards or a direct PayPal payment. Check for the latest points total as it seems to shift frequently.