How fast are different buses and components in a computer?
Wikipedia has a good page:
Observations: 10Gbits/s to 200Gbits/s seems to be the limit for transfer speed, depending on whether you are using copper, optics or RAM access over a short distance. Video cards go higher, not sure if that could be useful somehow outside of the realm of graphics.
Update 2016-04-05: There is a standard called Thunderbolt that is able to do 10Gbits/s, 20Gbits/s and in Thunderbolt 3 40Gbits/s. Thunderbolt seems to be mostly used to drive digital displaysand is mainly serial.
The fastest available SSDs seem to often max out at 5Gbits/s Best SSD 2016 - 119 Charts - UserBenchmark