User blog comment:AttackEyebrows12/Epic Rap Battles of the Whoniverse 1: The TARDIS vs The DeLorean Time Machine/@comment-28938497-20150323084347/@comment-28938497-20150323105055

Sixth Doctor vs Joseph (and his amazing technicolor dreamcoat)

Sontaran vs Krogan

Cyberman vs Cylon/Borg

The Master vs Khan

There are some ideas off the top of my head.