http://www.cavebear.com/CaveBear/Ethernet/
ftp://ftp.cavebear.com/pub/Ethernet.txt (text)
http://www.cavebear.com/CaveBear/Ethernet/Ethernet.txt (text)

Send updates to Ethernet-codes@Cavebear.com

type.html
vendor.html
multicast.html

There are also less complete lists maintained by IANA and the IEEE.  IANA's is less complete because it is not aggressively maintainted; IEEE's because some entities apparently ask that their allocations not be publicised.

http://www.isi.edu/in-notes/iana/assignments/ethernet-numbers
http://standards.ieee.org/regauth/oui/index.html