Mac OS X only: Free, open-source application GlimmerBlocker adds a new preference pane to your System Preferences that brings system-wide ad blocking to your Mac. Just install GlimmerBlocker and let it do its work. You can add custom filters, track your ad-blocking history, and even allow your iPhone or iPod touch to use the GlimmerBlocker filters on your network. Firefox users already have the beloved Adblock Plus extension, but if you ever use a different browser or you'd prefer to manage your ad blocking through a robust preference pane, GlimmerBlocker does the trick. GlimmerBlocker is a free download, Mac OS X Leopard only.