The creators of Installer.app have released an easy-to-use utility called IPhoneInstaller that will hack your iPhone and add Installer.app. From there, you can easily add more programs to your iPhone by running Installer.app.
IPhoneInstaller will only run on macs right now, but both Intel and PPC Macs will work. No plans for supporting Windows have been announced.
New! We now have a single command Mac (PPC & Intel) installer for Installer.app, get it here. This will automate the entire jailbreak and Installer.app installation process for your 1.0 or 1.0.1 iPhone, including automatically downloading the right firmware files. Be sure to read the short README file for installation instructions.
If possible, it is recommended you do a full restore of your iPhone using iTunes before installing this, but this is not required — it will simply make for a cleaner install.
