Rhododendron and Azalea make a bright splash of colour and come in all sizes from compact to tree sized.Azaleas tend to be smaller in size and often more garden sized but both have the same growing requirements.
Aquilegia are a late spring flowering, herbacious perennial. Aquilegai are very easy to grow, often self seed and come back reliably each year. They come in a vary large range of colours - images and growing tips
Aubretia is a long flowering perennial in bloom throughout April and May. Easy to grow. It is an ideal trailing plant for a wall or bank. It does benefit from periodic pruning to prevent it becoming leggy, Video advice how to do this.
Tulips flower from March to May depending on the variety. Most Tulips are best treated as annuals although some, Darwin types, repeat the flowering year, more info.
I could never have a garden without Alliums. Most are spring flowering, and usually shades of purple, white and blue and easy to grow, returning reliably each year. Allium is a bulb which dies back completely over winter. Images, growing tips and planting combinations.
If you want to bring wildlife into the garden our native Hawthorn is a good bet. It is home to many insects, loved by pollinators and the berries provide fruit for a number of birds and small mamels . This time of year with the May blossom it looks fantastic.
There are many varieties of primulas flowering in spring from the simple native primrose, illustrated, to its blousy cousin Polyanthus.