Battlefield 3 will naturally include plenty of close combat weapons, chief of which are shotguns.

The Remington 870 is the main shotgun used by the US forces. It was introduced back on 1950 and is still in use today, both by armies and by private owners as well. The shotgun has been featured as the main shotgun of the US forces in numerous Battlefield 3, and is set to reappear in Battlefield 3.
Saiga 12

The Siaga 12 is a Russian-made semi automatic 12 gauge shotgun based on a modified AK-47 loading mechanism. It was first featured in Battlefield 3 and has since appeared in Bad Company 1 and 2. The Saiga 12 is expected to be back in Battlefield 3.

Italian-made SPAS-12 is a pump action combat shotgun used mainly by the US Army. It was featured as an unlock in the last few Battlefield games, and will reappear in Battlefield 3.

The USAS 12 is an Korean-made fully automatic shotgun which uses 12 or 20 round magazines. It was introduced in the 1980s for the South Korean army, and has since been adopted in several armies around the world. The USAS 12 is set to be back in Battlefield 3, most likely as an unlock.

The DAO 12 is a South African-made semi automatic, drum fed 12-gauge shotgun which appeared in Battlefield 2 and is set to return in Battlefield 3, as part of the Back to Karkand DLC expansion.