This is a complete list of the Assault Rifles that will appear in Black Ops 2. This information came from those who got to play the multiplayer at Gamescom:
The AN-94 was developed in Russia. It has been in service since 1997. It has an effective range of up to 700 meters and it can rattle off 600 rounds per minute. This was one of the assault rifles to make an appearance in the multiplayer reveal trailer. If you remember correctly, this gun was used by the player who was firing at enemies via a hole in his Assault Shield.
The SMR appeared in a few of the multiplayer videos that were put up on Youtube this week. This doesn't seem to be based on any real life weapon. Because the game is set in the future, this has given Treyarch the flexibility to create fictional weapons.
This appeared in the trailer reveal. The M8A1 is based on the XM8 assault rifle, which was developed by Heckler & Koch. It's gas-operated with a rotating bolt and it can fire 750 rounds per minute. In-game, it seems to be a burst-fire / select-fire weapon that shoots 4 rounds per trigger pull. It has low recoil and a reload time of about 3 seconds.
Not to be confused with the Type 95 that appeared in MW3. In Black Ops 2, the Type 25 is an automatic bullpup Assault Rifle. Fun fact: A similar-named weapon also appeared in the Halo series. In-game, it has low recoil and it carries 30 rounds by default. Like many of the other weapons, I have been unable to find a real-life version.
The SA58 is a weapon that is closely related to the FN FAL. The name SA58 is pretty ambiguous though, as there are about 20 or 30 real-life assault weapons that have have a similar name. Here's a picture of what the SA-58 potentially looks like:
In real life, the Sig 556 is actually a commercial variant of the SG 551 that lacks full-auto capabilities. It was developed in Switzerland and has been in service since 1990.
The SCAR-H first appeared in MW2. After seeing the multiplayer footage for Black Ops 2, I think it's safe to say that it'll be one of the Assault Rifles in the game. In case you didn't already know, the H stands for Heavy. In real life, it has been in service since 2009. In previous games, the SCAR-H was a powerful Assault Rifle that had a low rate of fire.