There are many easy perennials.Hardy geraniums come in a range of flower colours and many remain evergreen too. Shrubs such as skimmia, euonymus, the cornus dogwoods are easy too.

heathers, pieris, small acers, dwarf conifers... it really depends how you want your garden to look as there are also delpiniums, lupins and all the other herbaceous perennials.

Second vote for geraniums. Bulbs are also low maintenance and colourful, like alliums.

I'd just like to say that Pieris forest flame isn't a perennial, its a shrub, so if you want more shrubs that are easy care, there are lots to choose from - depends whether you want shade or sun loving shrubs though.