Winter flowering heather (erica carnea) provides an unexpected splash of pink in March when everything around it is still rather brown and drab. It can grow, when well established, to about 4 feet across. Mine started flowering at the end of January and the bees have been visiting every sunny day since. Im not really a big heather fan and find the pink a harsh colour in the garden but as a bee-plant its top value!
Unlike summer heathers these ones dont need an acid soil to thrive and will tolerate a wide range of conditions. So if you have a scrubby patch were you want some low growing, low maintenance flowering plant that will also support the bees this might be a good option.