Just made the switch to Android 2 months ago, from a Blackberry. Bought a Galaxy S3, and love it. A few of the apps I use all the time:
AntiVirus - Lookout Antivirus. It's small, realtime scans, and has never yet had false positives (so far). They update it frequently as well, and have good support, and best of all it's free.
Anti-Other - Lookout Ad Network Detector. Scans installed apps and lets you know which networks and pushes they have, and what information the apps can glean from your phone (and send to the web). Very useful, as I tend to download and try alot of apps.
Tasks - Advanced Task Manager. Nice and small, streamlined, and easy to use. Lets you customize which apps to kill, and which to allow to run. One tap kill widget makes it super easy.
Internet - Google Chrome. Used it to replace the stock browser almost immediately. It's faster, better laid out, and sync's with your PC Chrome, so you can seamlessly continue reading the page you were on when you have to leave, etc.
News - FlipBoard. It's a stock app with the S3, but is very good, nicely laid out, and has a good mix of interesting stories.
- Red Orbit. Mostly science, space, and tech news. Updated regularly, quick on my LTE connection.
Cheers.