I don't know if the Diablo 3 Auction House deserves it's own thread, but I know some of us spend as much if not more time in the AH than playing in the actual game. It's my opinion that you need the auction house to progress deep into the game, not to mention there is the real possibility to make actual money from using it wisely. So feel free to post theories or trends that you see to help out your fellow Chud brothers and sisters.
So I guess I'll start. Been buying and selling a lot of chest armor recently. Anything with 125+ vitality, 60+ all resists, and 600+ armor sells pretty quickly I have found. If I can find pieces with those stats for 300k or under, I usually buy em and flip em for twice or 3 times as much. Even better if you get a) sockets b) a second attribute (dex, str, int) c) life regen (300+). Obviously there are more exotic stats that can sweeten the deal: gold find, magic find, damage reduction etc. In general I would say All Resist is mandatory for Barbs and Monks. Glass cannons will probably look at high Dex or Int and the resists won't be as important.
My biggest profit came from an amulet that I initially won an auction with no BIN. I paid close to 900k for it. I never paid that much for something that I wasn't going to use, so it was a bit of a risk, but I knew it would sell. The stats were something like:
50 resist all
175 Life on Hit
30% crit damage increase
Those are 5 premium stats. Anything with 5 premium stats is going to sell. So pretty epic for a monk and pretty great for a Demon Hunter.
I looked in the AH for comps to set a price. Alot of ammys had more Dex or Vit or AR or LoH, but not alot had em all together like this. I put it up for 3.9 million BIN. It sold in about 3 hours. I probably could have gotten more for it, but I was happy with the proffit and used it to purchase other gear to sell.