What is a good fast lens for low light photography?

I have a Canon EOS Rebel T1i. I'm leaning toward the Carl Zeiss Planar T 1.4/50 ZE but it's a fixed focal length and I'm not sure if that's the best for concerts and stage events. However I've been a big Zeiss fan since I got my first vintage Rolleiflex with Zeiss lenses. Would one of the Canon lenses be better for a lower price point?