While I was hoping to get an Aimpoint unit on my AR 9mm soon than this, financially that isn't going to be the case.  So instead of fondling this beauty in my living room, I'd like to get a set of iron sights and start shooting it now.  What are some of you guys using?

I've got MBUS pro on one rifle and the plastic mbus on my 9mm. They both work great.

My favorite combo and on both of my go-to AR-15's is Kac micro rear and DD fixed front sight.   DD fixed rear is also good. I prefer the fold down rear If there's a likelihood of optics being mounted in the future, but fixed rear works fine with a red dot as well.  Both are similar price if you get the Kac on ebay.  These are basically the best you can get at any price IMO and can be had for about 120 for the set either way.  

Of course I also have rifles with mbus plastic on them and they're fine, but don't give me that warm fuzzy feeling.  LMT also makes good sights but the huge Thumbscrew is kind of an eyesore and can get in the way of flashlights.  

Fixed is better than flip up for a primary iron sighted gun imo.

I went with the Troy fixed sights . Around 100 cannot be beat .

DD fixed front/rear sights for me. Can be found for $113 shipped from Aim Surplus last I checked. I prefer fixed sights for rifles that I wont have an optic on.

Thanks for the homework assignment! LOL  I checked out all the different brands you recommended and so far I have to say that Troy sights appeal to me best.  Their profile seems compact and streamlined based on the images viewed.  Since I'm definitely getting an Aimpoint at some point, it would be good to be able to have the option of using both it(the Aimpoint) and the irons.  

One further question: Right now I'm leaning toward a fold down rear and a fixed front.  Would this be a wise choice or is a fold down front front a better idea?

Just get the DD fixed front and back.  Less to go wrong.

Down the road you can mount your aimpoint micro in a 1/3 cowitness mount.  Perfect for fast shooting, then snuggle down to the charging handle and bring the irons into play for the longer shots.  win-win.

I went with fixed Troy Tritiums front and rear.  I shoot MOA targets 66% IPSC targets and find hits are easy out to 100, although the front is getting pretty big in relation to the target at that point.