Many, if not most, of the newest and updated Linux applications out there are crafting Ubuntu/Debian-ready .deb packages that require just a double-click to install, but many apps are still available only in the .rpm files used by Red Hat and Fedora-based distributions. The Ubuntu Unleashed blog has a quick and simple tutorial on installing the Alien conversion tool and using it to convert packages to .deb format. Once you've got Alien installed, the command is simply:
sudo alien -k name-of-rpm-file.rpm
Note that this won't work for programs that are designed to utilise specific Red Hat/Fedora functions, but will save you a good deal of digging for alternate files.