FileHippo's Update Checker might not be as thorough as SUMo or as security-minded as PSI, but Update Checker is certainly easy and intuitive to use, and should be enough to keep your everydaysoftware, such as browsers, media players, etc, up to date. Its major limitation is that it bases its update recommendations on FileHippo's own download database. Simply run the scan, and it will tell you if any updates have been posted on FileHippo, and provide you with a link to the download page. Given that FileHippo hosts a lot of software downloads, ranging from the ubiquitous to the obscure, there's a fair chance that your software is covered. Minimalist and unobtrusive, Update Checker is great for the casual user looking to check for updates every so often.
Editor's Note: Update Checker can also detect portable software and search for updates, though you will have to add the portable folder in the "Custom Locations" search space.