More often than not dining room furniture will consist of a table, chairs, and a buffet or sideboard. Depending on the size of the room there can be more pieces, but very rarely is there less.
The purpose of a buffet or sideboard is to provide storage for extra dishes, flatware and linens, and also to serve as a surface area for placing dishes of food and/or decorative accents.
Buffet and Sideboard Styles
Buffets and sideboards (the two terms are often used interchangeably because they're basically the same thing) are available in a huge variety of styles. From French country, to classic Georgian, to urban contemporary, no matter what your style you'll be able to find a piece to suit. Just be sure to get something that will fulfill your needs, whether it's a particular style, a certain amount of storage, or some other criteria.
Keep in mind that you can also use a different piece of furniture in place of a traditional sideboard or buffet. If you have a chest of drawers or console table that looks good and serves your needs don't be afraid to use it.
Open vs. Closed Storage
Many people err on the side of formal when it comes to dining room furniture, and if this is the case it might be a better idea to go with closed storage (meaning a piece with solid doors). Closed storage is also easier because you don't have to worry about displaying the items within nicely. You can leave it a mess and close the doors.
A sideboard or buffet that consists of open shelving is airier and has a lighter feeling than a heavy, closed piece, but should you choose to use one keep in mind that you'll have to keep the things stored on the shelves looking nice. Given that people's formal china and linens are often very nice, this isn't necessarily a tough thing to do, but just keep it in mind when shopping.
If you're having a tough time deciding between the two you might want to consider a piece with glass doors. They're not as visually heavy as solid doors, and they still cover some of the items inside so you kind of get the best of both worlds.
Dining room furniture is often available in sets and if you choose to purchase one you won't have to worry about the sizes not relating to each other. However if you prefer a more eclectic look you'll want to be sure that the pieces work together in scale, if not in style. When purchasing a sideboard or buffet remember that it should be a bit higher than the dining room table. The most common height is 36".
Widths and depths of dining room buffets will vary, but make sure that it balances with everything else in the room. A huge table accompanied by a tiny buffet will look a bit disjointed, as will a small table with a very large buffet.
The most important thing to do when choosing dining room furniture, whether it's a sideboard or something else is to make sure that it's functional for your household and serves your needs.