SPDT switch controllable by GPIB
Since you're talking about GPIB, I'll assume you are interested in test automation. Key parameters to look at when evaluating a switch in a test automation application:


Number of channels - GPIB-controlled switch cards are available with up to 300 switches per card, and multi-card controller mainframes are available that can contain 1000's of switches.
Frequency band - can the switch pass all the frequencies in the signal you are switching. Switches are available for "low frequencies" (maybe 10 or 100 MHz) and for RF (3, 6, 18, 26, or higher GHz). 
Current handling - if you are switching power lines carrying more than say 1 A, be sure the switch can handle the current.
Cycle lifetime - A mechanical switch can only be switched so many times before it wears out (typically defined by on resistance increasing above the spec level). This could be on the order of 1 to 5 million cycles for good quality switches, but its still a number you could exceed within a year if you are switching multiple times for each device tested.
Price - if you haven't bought GPIB or RF gear before, be prepared for sticker shock.


Agilent and National Instruments are the top-tier vendors for this kind of equipment, and each offers many types of switch. 

You mentioned you want a "fast" switch. If you are talking about the signal frequency, you can probably find a switch capable of microwave frequencies and a (separate) GPIB interface to control it. If you are talking about the switching time, I've rarely found that the switching time of the switch itself is significant compared to the time required for GPIB communication. However if you are doing, say 6-1/2 digit voltage measurements on the switch output, you will need to be concerned about the settling time after switching -- in that case consider using one of the switch control units with a built in multimeter and look carefully at the settling time of the switches you choose. 

Also, consider alternative interfaces. It's very likely that if you need less than 10 low-frequency switch channels, you could find a lower cost solution using USB control instead of GPIB. You might find an integrated USB-controlled switch or you might need to use a USB digital I/O device to control a simpler switch device.