Apkworlds.com is probably the best APK download site for Android.
Employees review all APKs uploaded to the site before publishing. The site matches cryptographic signatures of newer versions of applications with previous versions (to make sure they were signed by real developers). Brand new apps are compared with other apps from the same developer to ensure they are genuine. The bottom line is that if apkworlds is unable to validate the APK file, it won't publish it. Therefore, on the site you will not find any modified APKs, pirated or paid applications.
For each app, you can grab older versions, view information pulled from Google Play, and access a list of related apps. If an app that you install with apkworlds receives an update from Google Play after you've installed it on your device, it will automatically update to the latest version.
