Here is a very interesting design from Reinier de Jong featured in dezeen magazine:

REK coffee table by Reinier de Jong
"This coffee table by Rotterdam designer Reinier de Jong can be expanded by sliding the middle sections outwards in either direction.
REK coffee table by Reinier de Jong
The top and two sides are finished in white while the edges are veneered in oak, birch or beech. Stoppers prevent you pulling the inserts too far.
REK coffee table by Reinier de Jong
REK coffee table by Reinier de Jong
See more work by Reinier de Jong here.
REK coffee table by Reinier de Jong
Here are some more details from de Jong:

REK is a coffee table that grows with your coffee needs. When you have visitors, just get some chairs and extend the table any way you like. Enough space for all those coffee cups and store your book or knitting set in the spaces underneath the tops.
REK coffee table by Reinier de Jong
You can extend REK in various ways. Built-in stops make sure you will not extend the sliding parts too far. Of course you can also put REK in a permanent position that fits your interior.
REK coffee table by Reinier de Jong
The top and two sides of REK are white HPL and the edges are finished with your choice of parquet wood: oak, birch or beech. The end grain side of the wood is beveled in order to get a grip: a subtle detail.
REK coffee table by Reinier de Jong
The dimensions of REK table obviously vary with its configuration. REK is 60 by 80 cm in collapsed state, its maximum lenth is 170 cm and its maximum width is 130 cm.
REK coffee table by Reinier de Jong
REK coffee table is related to another REK by Reinier de Jong Design: the bookcase that grows with your book collection.
REK coffee table by Reinier de Jong
Reinier de Jong is designer and architect. He designs furniture, interiors, houses and other buildings. He is best known for some furniture designs like REK bookcase, KEER chair and VOLT table."

Source: http://www.dezeen.com/2012/02/02/rek-coffee-table-by-reinier-de-jong/