Hi all, sightings of bees (particularly bumblebees) in winter are becoming more common, so try to have something in flower for any that visit your garden. They won't find much sustenance in winter pansies, I'm afraid! Try winter-flowering clematis and honeysuckle, daphne, mahonia, heather. And if you find any bumblebees that look like they're struggling to fly, you could make them a solution of sugar and water (equal prts of each) to give them the energy to fly.
Looking to spring and summer, make sure you have plants in flower all year long. Favourites include red clover and viper's bugloss, but a more comprehensive list is available from the Bumblebee Conservation Trust here