This is Gahmah here, and I have a created a list of what I know is going to be in Forces of Corruption, the first expansion pack for Empire at War.

(Note: This isn't everything, this is almost everything I've learned judging by the trailer, the summary, and the screenshots.)

Units:

Tyber Zann - some underworld figure who fights both Rebels and Imps, as well as the forces of his rival, Jabba the Hutt.

IG-88 - Oh yes! Uses IG-2000 in space.

A Nightsister with a lightwhip.

Yoda - That crazy elf leaves his home and enters war once again.

Luke Skywalker - I think he's going to be able to be used on land this time.

Plasma Tanks - In the trailer, we see a group of them take out an AT-AT with ease.

Zann's thugs - basic infantry for Tyber's crime organization.

Dark Troopers - we get to see them for what they really are when compared to their cousins (assuming that droids can have cousins, which they don't) in the Battlefront series. Nice guns! Nice armor! Nice everything!

Juggernauts - for the people who are confused by the name, this is also a Clone Turbo Tank. Yes, fear the freakishly huge APC!

Droidekas (Destroyer Droids) - Apparently, these things weren't shut down after the elimination of the CIS. I guess not all of them were connected by the control signal. If you watch the movies, you'd know why to be afraid of these things.

Tie Interceptor - Oh Yeah! The dagger-winged threat in space from ROTJ is here.

B-Wing - Another Oh Yes! The strangely designed other fighter craft of the Rebellion.

Star Vipers - Basically, they are the same ship design of the Virago, which is owned by Prince Xizor, the current head of Black Sun.

The Executor - Double Eek! (single Eek was the Imperial Star Destroyer) Darth Vader's Super Star Destroyer. That thing is HUGE! I bet it would take more than one Mon Cal Cruiser (and many Y-Wing squads) to destroy it.

The Death Star 2 - I don't know about blowing up planets, but I know it will be able to blow up capital ships (in the original game, the DS1 could only be used to blow up planets, which primarily because of the firing-time factor). Yeah, be afraid.

Eclipse Star Destroyer - Triple Eek! Biggest. Star Destroyer. Ever. If you thought the Death Star was a scary sight, you gotta see what this thing can do! This thing is a true capital-ship-killer!

Planets:
Felucia (I wonder if they're going to put man-eating plants there)
Saleucami
Hypori
Mandalore
The Maw
Honoghr (I wonder if there are going to be Noghri)

That's all I know of for now. If you know anything else let me know.

BTW, it is Blogiversary Eve today.