PCI & ISA speed
ISA ~8MB/sec, as I remember
PCI:
PCI32 33Mhz 32bit * 33Mhz ~ 133MB/sec (desktop variant)
PCI32 66Mhz 32bit * 66Mhz ~ 266MB/sec (server)
PCI64 33Mhz 64bit * 33Mhz ~ 266MB/sec (server)
PCI64 66Mhz 64bit * 66Mhz ~ 533MB/sec (server)
PCI-X (also server bus):
64bit 133Mhz => 1066MB/sec
64bit 266Mhz (DDR) => 2.1GB/sec
64bit 533Mhz (QDR) => 4.3GB/sec
PCI-Express (successor of PCI)
PCI Express Link - Bandwidth
x1 0.5GB/sec
x2 1.0GB/sec
x4 2.0GB/sec
x8 4.0GB/sec
x12 6.0GB/sec
x16 8.0GB/sec
x32 16.0GB/sec
note: MB=MegaBytes, GB=GigaBytes
PS: also there are many buses (such as VLB, EISA, MCA) but they aren't so common as buses described above