You can browse the Ceylon Herd repo, or view the current module list, and even search for a module, using the menu at the top of each page.
$ ceylon compile --rep https://modules.ceylon-lang.org/repo/1/ com.acme.module $ ceylon doc --rep https://modules.ceylon-lang.org/repo/1/ com.acme.module $ ceylon run --rep https://modules.ceylon-lang.org/repo/1/ com.acme.module/1.2