anything in the juniper horizontalis family ...

and those would be conifers... and perhaps you will get a better answer in the conifer forum ... or maybe not... been pretty dull over there .. lol ...

ken

What about a prostrate form of ceanothus? Lovely blue flowers in the spring, attractive tiny leaves, evergreen. I've only had mine for about a year, but I'm pleased with it so far.

Ceanothus won't survive a zone 5 winter. A similar but less common approach than the juniper is Microbiota decussata, Russian or Siberian cypress/cedar. This is groundcovering conifer with a soft, feathery appearance. Extremely cold hardy, it develops an interesting plummy copper color in winter.

Here is a link that might be useful: Microbiota decussata

Not quite evergreen, but close is Rockspray Cotoneaster (horizontalis). I find that it is green until it is so deep in snow that you can't see it anyway, and perks right back up in early spring. A bonus is the red berries (self-fertile) in the fall. Mine gets to be about 2 1/2 feet tall and it spreads quite a distance.

Then there is creeping phlox, if you want something that is really short.

Here is a link that might be useful: Rockspray Cotoneaster