Re: AR 15
Hey. By "stationed" I take it to mean that you're serving in the Armed Forces.
I'm actually building an AR-15 together for a friend in nearly the exact same position as you.
If you're buying, your best bet at this point is to purchase a boutique AR-15 from a reputable builder. Large to medium size builders (Larue, Daniel Defense, BCM, even Noveske) are clogged up with insane backlogs. There are constantly new developments in ARs however and manufacturers are announcing new products constantly. For instance, you can order a Legion Firearms 7.62 semi-auto and expect it to be delivered within 20 weeks:
http://store.legionfirearms.com/SearchResults.asp?Cat=1814
If you're building, your first challenge is going to be not getting absolutely raped on the cost of the lower ($400 panic price), bolt carrier group (insanity - about $300 - $450 panic prices) and lower parts kit (again insane - $150 - $200 without trigger). For some reason, these are the hardest pieces to acquire. I've been looking pretty regularly at ARF, M4carbine and of course SH for these pieces and they go fast for ridiculous prices. $800 for a stripped lower with a highly desirable rollmark (e.g. Colt, Noveske) is not unusual.
Keep an eye out on manufacturers of lower receivers. Aero Precision, for instance, which does manufacturing for Armalite, just did a run of stripped AR lowers. They sold out within a day, of course, but for that day, you could get a stripped lower for $200. Armalite will also sell all the parts you need for a complete lower build. You probably have a replacement kit somewhere for your issue M4 from which you can cannibalize springs and detent pieces.
Upper receivers are rarer but still available for decent prices. Barrels, too, though the very high end (Noveske, Shilen, KAC, WOA, BCM hammer forged, Krieger) are enjoying slightly higher premiums if anything.
Don't buy a used AR. Every asshole with a rusted up Oly Arms in their closet is CLP'ing his poor old rifle up and attempting to sell it for five grand with a some mall ninja Magpul crap on it.
Trade your mags. They hand you mags like candy. In the world, a $50 30-round mag is "normal" today.
edit: oh, and also, thanks for your service