<a href="https://github.com/Roll20/roll20-character-sheets" rel="nofollow">https://github.com/Roll20/roll20-character-sheets</a> has all of the community character sheets, and <a href="https://github.com/Roll20/roll20-api-scripts" rel="nofollow">https://github.com/Roll20/roll20-api-scripts</a> has most of the completed API scripts. The majority of the sheets/scripts in those two repos are available from your game settings page (either when selecting your character sheet, or as a one-click install API script), but not every single one of them. The ones that aren't available from the Roll20 interface are generally either unfinished (for the API scripts), or early versions of alternate language sheets. As far as other user content goes, I'm not aware of any collection.