This is a fast and lightweight virus scanner. It works very well and has an included ad-ware dectector. But be aware, the detector cautions apps, that are clean and ignore apps, that really spam your phone. So I would not count on this feature. But for the actually purpose, it's rather well.
SD Maid & SD Maid Pro
A cleaning tool for your phone. Works very well. You can exactly see, what data it will erase and you can add exceptions. So, this app will only delete, what you want it do delete.
This is a simple app, that lists you all sent and received SMS. Very useful, when you have a flatrate and you want to keep ypur SMS capacity in sight.