There is the updates-testing repository which holds fedora 7 testing packages and the development repository which holds fedora 8 packages. You can enable them like this
yum --enablerepo=updates-testing
yum --enablerepo=development
You can also enable them through yumex and take a look at all the packages they contain.
However you may harm your system installing packages from those repos. Especially if you mix fedora 7 and development (fedora 8 rpms). You choose.