basically you can use any macaddres that is not used already.
however if you are a bit smart you would look for a vendor that you know you will not be using. fx if you have an all dell network with no APPLE computers, then use Apple mac addresses to minimise the risk of having problems with duplicate mac addresses.
The different vendors have different series.
http://www.coffer.com/ has a list
there are other lists out there.
Good luck
