This weekend on The iHeartRadio Countdown with Mario Lopez the incredibly talented Gwen Stefani will be checking in! She's kicking off another run of her Las Vegas Residency at The Planet Hollywood Resort and Casino and we're giving away a free trip on us! Flights, 2 night stay at Planet Hollywood, tickets to her 'Just A Girl' show and more! You can enter for a chance to win that right here!! Plus she's working on new music! So we'll catch up with her, countdown the top 20, play some of Mario's favorite throwback classics! Tune in!