The Kahtoola Microspikes that fimm linked to are great for walking on snow, ice, and the occasional stretch of bare ground. I put a good number of miles on mine today in Rocky Mountain National Park on everything from water ice to packed snow to the occasional bit of bare rock. Not sure if I would want to run in them on icy pavement, though, I would expect my shoes to slide around in them.
The Yaktrax are good for running on packed snow, but they're not nearly as durable as the Kahtoolas. The Nanospikes look promising- I may try a pair. I would expect anything from Kahtoola to outlast anything from Yaktrax.