As per Fedora News yumex (YUM extender) has now been added to Fedora Extras. yumex is a gui for YUM (Yellow Dog Updater Modified - used by Fedora to update/install applications). It's pretty easy to install:
$ yum install yumex
The other tool I tried is KDE's kyum. Although, I am now using GNOME, I installed it to see the interface. I found both yumex and kyum are pretty easy to use but yumex has a filter option which becomes very handy...
[UPDATE - 08/11/2005]
After using both for a few months, it looks like kyum serves me better. When I had an issue with one of the repositories, yumex kept looping and crashed while kyum just displayed the the error. Kyum interface does allow you to disable/enable repos easily too.
You can install both by typing
yum install yumex kyum