With Hal trying on all the rings (He even qualifies for a black ring technically), I still have a feeling that he's going to become the "White Lantern" Unifying all the rings and becoming the "Ultimate Lantern" or something like that.
So far, we've seen him with the Green, Yellow, Red, Blue and Orange (Not sure if this actually happened in comic or is just promotional image)

Has he had any of the other color rings on?

Not that I know of. I think you are correct on all accounts. I can't recall if he had an orange ring on, or if he just grabbed larfleeze's lantern for a minute, it wasn't long.

Wait I think he did have one on, I think I recall the ring telling him he wanted a bunch of stuff or something like that.

And soon, the Green Lanterns and the Yellow Lanterns will join together and form a new Lantern team. They'll be the Sprite Lanterns, cause then they'll be lemony-lime flavored.

That was the Lantern and/or some other force.

"Force"... Major Force should get a Red Ring. It'd suit him well.

Aw man, I just realized something horrible. The original idea behind the orange lantern corps is that their greed was going to leave them disfigured.

I just googled Agent Orange looking for a picture of Larfleeze. Really poor taste.

Poor taste? You sure that was orange and not Moxie? Oh, wait, that's soda flavoring I'm thinking of. My bad.

And how many Black Lanterns are there now?

are they going to include any LOS?

Karate Kid, who died recently. I don't think his body went back to it's proper time.
That's a possibility.

That shot of all the people Larfleeze killed having become Black Lanterns was hysterical.

I have a question/theory about Nekron. I am currently making a mod of him based on the spoiled Blackest Night #5 cover. I decided to make him into a giant fig even though I read a Geoff Johns interview somewhere where he stated Nekron is actually not as big as he appears on the said cover.

While making the custom, I realized Nekron has shackles and chains. If he is the "master" of the Black Lanterns, why would he have shackles? And why did DC "spoil" it so early by releasing that pic/cover? I have a feeling that, like the Anti-Monitor, Nekron is just a pawn and not the main bad guy. I believe that Geoff has something up his sleeve and that he's going to blow us away by the end of Blackest Night. I hope it's not Darkseid, though, with his friggin' anti-life equation.

What do you guys think? Is Nekron the guy behind the Blackest Night, or will it be someone else? Someone should start a poll so we can see what people's theories are.

Abattoir

Amon Sur

Aquagirl

Aquaman

Black Hand

Blockbuster

Deacon Blackfire

Deadman

Dolphin

Elongated Man

Firestorm

Flying Graysons

Hawk

Hawkgirl

Hawkman

Jack and Janet Drake

Jade

KGBeast

King Snake

Lilith

LOIS LANE (EARTH-2)

Magpie

Martian Manhunter

Pariah

Solomon Grundy

Scar

Spectre

Sue Dibny

Superman (Earth-2)

Tempest

Terra

Trigger Twins

Ventriloquist

There are millions of others across the universe but these are the ones with history in the DCU. Holly Granger (Hawk II) was recently killed by Black Lantern Hank Hall but it's unclear if she is just dead or if she'll "rise". Black Lantern rings have infested the crypts of Oa and the planet Xanshi has reformed to serve as The Black Lantern version of Mongo. I have no doubt there will more shocking additions to Black Lantern Corps. as Black Lantern Hawk Man called Ray Palmer to "talk". Black Lantern Rings have also been seen flying in huge swarms to every world that possesses a Power Battery converting the valued, respected, and honored dead of those worlds into Black Lanterns.
http://www.dccomics.com/sites/greenlantern/?cr=black