Dublin Bikes rental scheme, but I have been very impressed with the scheme whenever I do have a cause to use it. The only gripe I have about the system is that it is cumbersome to sign up and it typically takes several days to get a membership card. Unfortunately this means that the scheme can't be used by tourists visiting Dublin.
There is a similar scheme in many other cities. I see that the London cycle system recently added a facility for casual users to rent a bike without having to have an annual subscription. I wonder why Dublin bikes don't introduce a similar facility? I am sure tourists would love to use it to cycle around the city centre.