I picked the Big Finish Sapphire and Steel as my favourite spin-off so I'll go with something different here. I really like their range of 2000AD audios. I'm tempted to pick the Judge Death story because it has the fabulous Mark Gatiss as Judge Death himself but instead I've gone for a Strontium Dog audio drama.
Strontium Dog: Down to Earth has Simon Pegg as Johnny Alpha, Big Finish regular Toby Longworth plays Wulf Sternhammer and Jacqueline Pearce herself is the baddie. It manages to capture the mix of humour and action that the comic strip has and is good fun. In fact all of the 2000AD productions are.
Note to self, must find time to listen to more Big Finish.