Golly can download patterns, rules and scripts from these online archives:

LifeWiki Pattern Archive

Gliders in Life-Like Cellular Automata

Alan Hensel's Pattern Collections

Jason Summers' Pattern Collections

Rule Table Repository

Golly Scripts Database

Note that Golly stores downloaded files in a directory that can be changed via a button at the bottom of Preferences > File. You might like to change the download location to a directory visible in the Show Patterns panel (to the left of the viewport), then you can easily re-open a pattern or zip file without having to download it again. Also, downloaded patterns and zip files are remembered in the Open Recent submenu, and downloaded scripts are remembered in the Run Recent submenu.