I really like these rugs from Dash and Albert.
I came by them via this tutorial on how to lay your own stair runner.
They also sell these really happy tote bags (i.e. knitting bags) made out of their rugs!
I guess you'd have to be careful about dirt on stair runners but they also have indoor outdoor rugs that can be used.
They're very affordable and I don't think my brain is going to quit until I have a go at covering my stairs in some happy stripes.