Land Aid '04 is a common Sorcery card from Unhinged (UNH), collector number 102. Current market price: $0.25 (foil $2.17), TCGplayer market prices via Scryfall.
Search your library for a basic land card, put that card onto the battlefield tapped, then shuffle. If you sang a song the whole time you were searching and shuffling, you may untap that land.