I use Lookout, which is free. It does a lot. It scans APK's before installing. It also scans for virus and malware. Can do backups of contact, photo's etc. It also has a tracker to find phone. And an alarm if you lost you phone in your house. Lookout has gotten very good writeups.
Check it out for yourself, but I like it and it doesn't kill the battery.
Here is the Appbrain link and Lookout's own link:
http://www.appbrain.com/app/com.lookout
https://www.mylookout.com/