Mac only: There's no shortage of uninstallers for Mac OS X, but they all are basically the same drag-and-drop interface. TrashMe brings something new to the table, allowing you to also choose apps from a list and search for them.
Uninstallation has always been a point of annoyance for Mac users, since Mac apps leave system files lying around your computer but OS X doesn't come with any kind of uninstaller to get rid of them. Similar to AppZapper, AppDelete, AppTrap and AppCleaner, free app TrashMe has a simple interface, in which you can drag any application into its window to easily delete the app and its system files.
However, TrashMe also features a nice sidebar in which you can choose applications, widgets, preference panes and plugins from a list, not unlike Windows' built-in Add/Remove programs menu, saving you the trouble of searching out the app in Finder. You can also add other sources, like any folders in which you often save downloads (like your Downloads folder or the Desktop). You can even search your computer for installed apps if you don't know where they're stored, which is a huge advantage over the minimalist drag-and-drop interface of yesteryear, with which you'd have to Spotlight the app first. It really adds a lot of needed features to the uninstallation game, and still does a great job of uninstalling apps you don't want anymore (including, ironically, your old uninstallation app). Hit the link to try it out.
TrashMe is a free download for OS X 10.6 only.