File Share
From Halopedia, the Halo wiki
In Halo 3, you have a File Share, which lets you upload up to six different types of files. These file types include films, film clips, map variants, gametypes and screenshots. You can use the six for free, but to upgrade it to twenty-four it costs 750 Microsoft points.
Also, by becoming a member on bungie.net you get 18 free folders for a limited time to place whatever you want.
