In addition to ICs and sensors mounted on breakout boards and larger mbed baseboards with several connectors, there is a wide array of individual breakout boards commercially available to connect external devices that require a connector. Most of the breakout boards come with holes spaced by .1" for the connections to the pins. You can solder break away header pins like those seen below into the .1" spaced holes after breaking off a strip with the required number of pins.

The breakout board will then plug directly into a breadboard to make a prototype as shown below. The external device can then plug into the connector.

Individual Breakout boards are available with Ethernet, USB, CAN, PS/2, RS-232, microSD, audio, Smart Card, SIM, and VGA connectors. In some cases, the connector will need to be purchased separately and soldered to the board. The .1" breakaway header pin strips will typically need to be purchased separately.

They are available from a variety of vendors such as http://www.Sparkfun.com , http://www.SKPang.co.uk, and http://Coolcomponents.co.uk. In addition to direct sales, Sparkfun and Pololu also have a large number of distributors worldwide.