As the economic downturn has hammered companies’ advertising budgets, many businesses have turned to user-generated web content to get their messages out on the cheap rather than shelling out thousands of dollars to ad firms. Tech companies, including Amazon and Nokia, also are turning to crowdsourcing to spur fresh ideas, hosting contests this summer that ask the public to create everything from TV commercials to mobile applications in exchange for big money and other prizes.

Amazon, which traditionally hasn’t relied on ads to promote its business, is hosting a contest this summer that asks people to submit 30-second TV commercials. Contestants can win up to $20,000 in Amazon Gift Cards, and their winning commercial will be shown at the Gen Art film festival in New York. The contest is reminiscent of previous user-generated advertising competitions hosted by Heinz, Doritos and Dove, which the folks over at NewTeevee have covered.

A competition similar to Amazon’s just wrapped up at the Cannes Lions advertising festival, where contestants from around the world competed to create 30-second TV commercials for companies such as Nokia and Hewlett-Packard, the Financial Times’ tech blog reported. UGC advertising is the future, and ad companies better start embracing it, said film director Spike Lee, who judged the competition. “We’re going to come to a time very soon where…I’ll be paying whatever it costs to go to a theater and see a film that was shot on a regular digital phone,” Lee said.

Not much of a film whiz? Fear not. Many companies are holding contests to find the next big idea for business. Here’s a listing of some of them:

• Nokia is holding two sets of contests that offer contestants big money for creating mobile applications: “Calling All Innovators” and “Open Screen Project Fund.” The submissions deadline for the “Calling All Innovators” contest ends tomorrow.
• Netflix is in the final stage of its competition that challenged people to develop a way to improve its movie recommendations for a whopping $1 million prize.
• A new tech startup, called ChallengePost, is launching in beta today and is focused on providing a space where companies and individuals can create contests and award prize money for winning submissions, according to Venture Beat. The startup has raised $500,000 from angel investors, including Betaworks and Esther Dyson.