I can really recommend the idlers by TerraCycle. The stock idler on my Burley was half siezed up with the power side still turning but the chain mainly slipping over it. Put the replacement on an wow, what a difference!
Mind you, after riding some time with the idler half seized up and pullying and grooving over the plastic then replacing it with ANYTHING that actually turns with the chain and really noticing it is a bit like hitting yourself on the head with a hammer and thinking "man it feels good when you stop!"
But the idler from Terracyle, while not cheap, is really high quality! I'm sure it will last longer than I will!