You can use yum to update itself - that's absolutely fine.
By default 'yum list' shows you all the packages from all the enabled repositories, but you can disable a repository for a single operation with "--disablerepo=repository"
So this command shows all the available packages that *aren't* from Core, Updates or Extras:
su -c 'yum --disablerepo=base --disablerepo=updates-released --disablerepo=extras list'
Most repositories have hundreds or thousands of packages so add a grep on the end to only show what you're interested in:
su -c 'yum --disablerepo=base --disablerepo=updates-released --disablerepo=extras list' | grep -i 'what-i-want'
Yum has other search facilities, which are briefly covered in the Fedora documentation:
I tend to go to the Website of the repository when I want to just casually browse the packages.