If you have pre-ordered the Surface Pro 4 tablet and/or the Surface Book notebooks, but want to add more ports, you might want to consider getting Microsoft's Surface Dock that's been made especially for those products. Amazon is now taking pre-orders for the Surface Dock for $184.80, a small decrease from its normal $199.99 price tag.
The Surface Dock, which can also work with the older Surface Pro 3 tablet, contains two Mini DisplayPorts ports, four USB 3.0 ports, a Gigabit Ethernet port and an audio out port. It also includes a magnetic Surface Connect cable which, when attached to the Surface products it supports, allows for transfers of video, audio, and data files from devices that are connected to the Surface Port.
By the way, you can also pre-order the Surface Dock on Microsoft's Store site, but it has a full $199.99 price tag.