What lens should I use for low lighting and fast action without a flash?

I have a Nikon d80. I have three lenses, but my favorite one to use is my Nikkor 50mm f/1.8 AF. It shoots okay in low lighting without a flash.

I want a lens that will shoot well in low lighting and capture fast action without the use of a flash. Can anyone give me a suggestion?

Your 50mm f1.8 already does that.

There's a 50 and 85mm f1.4 but, honestly, in low light the difference is not that big. Really low light you're shooting wide open and with rather low shutter speeds. I see two solutions here, either upgrade your body to something newer, D7000 for example can produce images at iso6400 that would be useable with just a bit of cleaning up. Another option is to start using flash

I just got me a 50mm 1.8 for basketball… Were not allowed to use flash, it has been pretty difficult, but I would suggest putting it on TV and setting the shutter speed at 1/1500 and high ISO

What sort of fast action is it you want to capture? If it's anything that would be difficult to shoot close up, then you may need to look at longer focal length lenses. The big problem with this, is that fast, longer lenses prove to be very expensive, compared to f3.5 upwards. S/H fixed focal length lenses may be found at reasonable cost on Ebay.

You've answered your own question haven't you? You said your 50mm f1.8 shoots ok in low light without flash!

Or do you want something with more reach? Various options, but fast telephotos are not cheap. The 300mm f4 and the 70-200mm f2.8 spring to mind.