Golly can download patterns and rules from these online archives:

LifeWiki Pattern Archive

Gliders in Life-Like Cellular Automata

Alan Hensel's Pattern Collections

Jason Summers' Pattern Collections

Very Large Patterns

Rule Table Repository

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 Files panel (to the left of the viewport), then you can easily re-open a pattern or zip file without having to download it again. Downloaded patterns and zip files are remembered in the Open Recent submenu.