There is also AppMonster .

There is also AppMonster. It is available as both a free and a paid app (€2.96) on the Play Store. ES File Explorer is nice too (it gives more significant names to the backed up APKs) but AppMonster is better. I use both of them and AppMonster can back up apps that ES File Explorer does even not find (Seesmic Pro for example). I almost asked a question about "un-backup-able" apps on the site because of that.