I'm rather partial to the program Llama. It basically is like an automation program on some steroids. You can program a number of things to take place depending on various conditions, like time of day or even whether or not you're in a specific area. It does this using cell tower/mast IDs, which is not as accurate, but it's very battery friendly since your phone is pinging these towers anyway. Llama is just making use of data your phone is collecting as part of its normal operation.
For example, I have mine set up to switch on bluetooth when I am not at home or work, reasoning that I'm most likely in my car. And then when I get to work, I have it mute my ringer, and keep the notifications volume to a reasonable level. However, when I'm home, I turn the ringer back on and the volume up, etc. Takes a little time and effort to learn to program it, but it's worth it IMO, and it's free.
If you don't mind rooting your phone, you can then install something like the LeanKernel, which is a custom kernel where the developer stripped out all the junk not really needed on a cell phone, and did a little modest undervolting of the CPU, which I find gives quite a bit better battery life. If you root the phone, then something like ROM Toolbox or Titanium Backup can be invaluable for getting rid of a lot of the excess junk installed on the phone. Titanium Backup lets you "freeze" programs, which is basically preventing them from running, to see if any ill effects result before you uninstall the program. Rooting also opens up the possibility of custom ROMs which already strip out a lot of that stuff for you. The one thing to note, is that Samsung apparently has some kind of counter buried deep in the low level guts of the phone that keeps track of how many times you flash custom software on it. The odds of the average employee at a cellular carrier store knowing how to check that are probably minimal, but be aware that it's there.
Also, Sedio has a nice holster for the S3. It's designed to be used with a "naked" phone. It has a spring loaded lock, and then a belt clip. I tried using an Otterbox case and holster with the S3, but it just made it too awkward to handle for me, and the gap in the plastic cover for the home button just meant dust would be able to get under the plastic over the rest of the screen.