If they had to appear on the main roster for any lenght of time:
Scott Steiner
Tomko
Christian Cage
Gail Kim
Rhino
Kazarian (Never lost a match in WWE BTW)
Christy Hemme (OK maybe not but she's still my girl
)
If not:
AJ Styles (Offered a contract but he rejected)
Samoa Joe (Used as a jobber without a contract)
ODB (OVW)
James Storm (Wasent taken when WCW was bought out)
Potentially:
RelliK
Angelina Love