Ok like the title says I have to admit I don't reload but will start very soon. Natually I have questions.

Who makes the best brass for .223 (5.56), .45acp?
What primer brand do you recommend?
What bullet do you like for each and why?

Thanks for your help in advance.

What do you use for your AR carbines?

Have you been keeping your brass so far?
If so, just use that.
If you haven't been, since the brass is a major cost of ammo, it might be best to begin.
As for the best bullets, the rifling rate of the barrel will determine the best weight, length and design of bullets to use, anywhere from 55 to 75 grains or so.
After that it's all experimenting to find the most accurate and best feeding combo.

For the .45 most folks use either the 200 grain semiwadcutter, if it feeds well, or the trustworthy 230 grain round nose, either jacketed or lead.
.451 for the jacketed, and .452 for the lead usually works fine.

In the end, success in reloading is mostly in the details, especially for rifles.
Get a reloading book that explains these details as well as the procedures and loads for the best chance of success.
And spend time on the forums for detailed instruction, too.

Hope this help some.

45 ACP brass?  Federal or Speer, unless you want to step up to Starline.  But I strongly reccomend you stay away from Remington brass in this caliber. 

Seconded,  the Remington brass seems to be way too soft to reload very many times.  I load random S&B and Federal leftover brass for practice, Starline for bullseye competition.

Try different things.  I've tried bullets as light as 155 grain LSWC and a number of different primers and powders.  In general, I found no real difference between name-brand primers. 

My favorite (and most accurate) load uses Nosler 185 grain JHP bullets with Vihta Vuori N310 powder.  I found it has very light recoil and groups at 25 yards the size of a quarter from my Kimber.  Your mileage may vary.

223 in a semi-auto?  Six or seven usually before it's too beat up.  Straightwall pistol brass?  Shoot it 'til it splits or you loose it at the range.  Just don't use it for serious loads past about three runs.

.223:

For plinking:
We do old brass fired multiple times, with Varget, and bulk hornady 55gr SP with Cannelure bullets.

For accuracy:
Depending on twist (which you know all about Doc), I'd do something never or once fired Norma, Lapua, LC brass, and 62-75 grain bullets, probably Speer Match King BTHP. You can use Varget here too, it's just not the most accurate at full velocity (which most powders aren't). You'd probably have to look at a website more dedicated to shooting small groups to find out which powder is best here with enough velocity for the longer shots.

For SHTF:
I do a little of both (actually three). We have loads based on plinking, accuracy, and even Urban (40 gr V-Max). Basically anything will work in an emergency and you can do most work with the plinking and precise work with the heavy, accurate loads.

---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
.45

SHTF:
We prefer a classic here. A Hornady XTP bullet pushed at 850 fps. Accomplished with previously fired brass and Unique powder.

For plinking and back-up SHTF:
We did use Hornady's bulk HAP (Hornady Action Pistol) bullets that were still hollowpoints but cheaper than the XTPs. Now we're using Oregon Trail Cast as anything else is hard to find. They're accurate, still in 230 grain, and I imagine they expand/penetrate acceptably in an emergency. Shoot the brass until it's split or lost.

Really, though, because of price the plinking load is the most popular.

I have a follow up question (if I may)...

What are signs to look for on brass to tell if it has been used past its useful life; in other words, what should one look for to tell is the brass is too beat up?

Someone else might have a better answer, but I believe the first things to check for would be:

• loose primer pockets
• split case mouths
• thin walls near the case head (checked with a paper clip feeler)

So basically, if it looks funny:  throw it out?

The main thing (besides obvious damage)is how much the brass is "worked". That is, How often it has been fired (stretched) and then re-sized (which tends to make the brass longer) and then needs trimming. Eventually you will get head separation in rifle brass- a very bad thing. The main thing to do is keep good records of how many times the brass has been loaded. Most full length sized rifle brass will take at least half a dozen loadings near max pressure, and several more if you throttle back just a tad.
"Range" brass- just the stuff you can pick up and don't know exactly where it came from or if it's factory and only once fired- can get you in trouble.
For revolver brass it's pretty easy- old brass starts splitting at the case mouth.