I'm going to try my hand at this:
Comics that remain unomnibussed (after January 2014) are:
*Dawn of the Jedi 0-15
*KOTOR 36-50 +War 1-5 + Handbook (Handbook might be in one of the announced omnibuses; remaining issues will certainly be in volume 3)
*The Old Republic 1-6 + The Lost Suns 1-5
*Lost Tribe of the Sith: Spiral 1-5
*Knight Errant 0-15
*Jedi vs. Sith 1-6
*Jedi: The Dark Side 1-5
*The Clone Wars digests
*Clone Wars Adventures 1-10
*The Clone Wars Magazine comics
*The Clone Wars 1-12 + Free Comic Book Day 2009
*Darth Maul: Death Sentence 1-4
*Purge (original, Seconds to Die, The Hidden Blade, Tyrant's Test 1-2)
*Darth Vader and the... (Lost Command 1-5, Ghost Prison 1-5, Ninth Assassin 1-5)
*Dark Times 13-32 (it looks like Blue Harvest 0 will be in the Dark Times omni, but not the rest of that arc, I think)
*Agent of the Empire 1-10
*The Force Unleashed I and II
*Star Wars 1-onward
*Classic Star Wars 1-20 + The Early Adventures 1-9 + The Constancia Affair + The Kashyyyk Depths + Planet of Kadril (the old newstrips from the 70s and 80s)
*Jedi Academy: Leviathan 1-4
*Legacy 0-50 + War 1-6
*Legacy Volume 2 1-ongoing
*The Star Wars (not yet published)
*Star Wars Tales 1-24
*PhotoComics I-VI + Clone Wars
*Manga Episode IV-VI (four books each) + EPisode I (2 books) + Manga: Black and Manga: Silver
*Free Comic Book Day 2011, 2012, 2013
Note that the contents of Omnibus: Wild Space Volume 2 is fairly presumptive; I assume Wookieepedia has it right, but it isn't 100% official.
The Thrawn Trilogy, the Dark Empire Trilogy, and the Crimson Empire Trilogy hardcovers essentially count as omnibuses. I seem to recall Randy Stradley saying that those books wouldn't get the omnibus treatment.
The current list of comics at Wookieepedia (http://starwars.wikia.com/wiki/List_of_comics) is pretty accurate, I'd say. The things it does not include are:
1- Darth Vader and the Ninth Assassin 1-5
2- Legacy Volume 2 1-ongoing
3- Star Wars 1-ongoing (the new series)
4- The Star Wars 1-8 (the one based on the original drafts)
5- Dawn of the Jedi 11-15: Force War
I think that's it.
Note that the November 2013 solicitations (which included the announced Omnibus: Dark Time Volume 1 and Omnibus: Adventures for January 2014) is the first to include two omnibuses.
I've bought every omnibus there is, even when I own everything in it in issues or TPBs (omnibuses are easier, and it means I can give issues or TPBs away to family later). I'll be skipping Adventures though, just because I like the digest books as they are.
It was the year of fire… the year of destruction… the year we took back what was ours.
It was the year of rebirth… the year of great sadness… the year of pain… and the year of joy.
It was a new age. It was the end of history. It was the year everything changed.
The year is 2261.
The place: Babylon 5.